Warlock Nezarec's Sin Build
I've taken to calling it "A Stab in the Dark," because I usually don't know what I'm doing when it comes to buildcrafting.
Thanks to the Charged with Light seasonal armor mod system, we have new ways of wreaking havoc on majors and bosses in PvE - the new mod "Lucent Blade" provides a 35% damage buff to your swords for 5 seconds after dealing damage with a sword, and consumes 1 stack of Charged with Light to do so. This build started with the idea of trying to maximize that perk's effects, and thanks to Nezarec's Sin and some new and returning artifact mods, there's a lot of synergy here. Also, this build can leverage Recluse which will be sunset next season, so it may be one of the last times to use the gun with a build like this at a high power level. It does rely on this season's artifact mods, so it will only work until the start of next season.
This build will allow you to do the following:
Counter all three Champion types on your own.
Use your sword to clean up yellow bars and bosses all day with big DPS buffs and lots of ammo - you won't miss your favorite special ammo weapon as a result of the Champion mod system.
High survivability thanks to Devour in bottom-tree voidwalker.
Very fast ability and super recharge thanks to the Nezarec's Sin exotic helmet.
Build Armor Specs
Top stats to spec for would be Discipline for increase grenade recharge rate (synergizes with the Oppressive Darkness and Overload Grenade mods below), and Intellect for your super. Armor element types listed below are required for the selection of mods to work. Total Energy is listed in a range from minimum required to total recommended based on my notes for each mod in the table below.
There's a very heavy emphasis on strong and unique mods from the seasonal artifact and seasonal activity. Standard weapon improvement mods are mostly restricted to sword ammo finders and scavengers to ensure you're always ready for DPS, and some optional Discipline mods and Boss Resist to help with grenade recharge and survivability.
Keep in mind you'll need armor that can equip the appropriate seasonal mods. Armor from this current season appears to allow for Charged with Light mods from both season 11 and 9 to be equipped right now. Also, season 10 armor appears to allow you to socket season 11 CwL mods that you have not yet purchased - not sure what the deal is there but it's likely a bug in our favor.
UPDATE: After many suggestions in the comments, I'm adding notes here for a build that uses the Gnawing Hunger void auto rifle that's targetable this season with Umbral engrams. It's an in-meta 600 RPM AR with void damage, and can roll demolitionist. To make the general structure of this build work with Gnawing Hunger, make the following changes to the leg armor in the table above:
Change leg armor energy from Arc to Solar.
Replace the Swift Charge  mod with the Sustained Charge  mod.
Replace the Sword Scavenger  mod with an Enhanced Sword Scavenger  mod, or if you prefer, an Auto Rifle Scavenger  mod.
You now have 2 extra energy to play with in the general mod slot. You can keep Boss Resist , or upgrade to other stat-boosting mods like Discipline  mod if you like. With a demolitionist void weapon though, grenades shouldn't be hard to come by at all.
Build Weapon Recommendations
The weapons here seek to get the most out of Nezarec's Sin's perk to give you faster ability charge rates for void kills. For this reason, you'll want to rely on your void weapons as much as possible for killing enemies. However, they're also aligned to the Champion mods and the Charged with Light mods. The pulse rifle will stagger Unstoppables (thanks to an armor mod this time, not a weapon mod), the SMG will pierce Barriers (using a weapon mod), and both will contribute to earning stacks of Charged with Light when you get rapid kills with them (more applicable to the SMG).
Requirement: Any pulse rifle
Top Recommendation: Outbreak Perfected - Exotic
Otherwise, your favorite pulse rifle should work fine here, not a big deal. You'll probably only be using this to stagger unstoppable champions.
Requirement: Any void submachine gun
Top Recommendation: Recluse - for obvious reasons
Runner Up: Every Waking Moment - target farmable on the Moon
Notes: Recluse is the obvious go-to weapon here for its Master of Arms buff - better damage and reload speed. But if you don't have it, or want to try something else, Every Waking Moment is an excellent option. It's also a void SMG, but it can roll with Demolitionist, and it's easily targeted for farming on the moon by getting the Essence of Obscurity from the Lectern of Enchantment. Demolitionist will improve your grenade recharge rate on top of Nezarec's Sin, so if you want to spam grenades with this build then this gun is worth a look. Make sure to put on an anti-barrier rounds mod from the seasonal artifact to counter barrier champions.
UPDATE: Alternatively, you can use a Gnawing Hunger void auto rifle with the demolitionist perk and anti-barrier rounds to really get grenade spam going. This might even be more effective than recluse given how good 600 RPM ARs are in the game right now. You'll need to make changes to the recommended armor to continue to gain CwL though, make sure to read those notes above.
Requirement: A void sword with Relentless Strikes and Whirlwind Blade
Top Recommendation: Falling Guillotine - new this season
Runner Up: Steel Sybil Z-14
Notes: The sword perk combo of Relentless Strikes and Whirlwind Blade has been the god-roll for DPS for a while, and that doesn't change here. Whirlwind Blade stacks 6% damage buffs for each sword hit up to x5 for a 30% total buff, which itself stacks multiplicatively with the 35% damage buff from the Lucent Blade armor mod. Relentless Strikes returns ammo to your sword after two light attacks. The reason I give the edge here to Falling Guillotine is that the heavy attack is a spin move which might damage multiple enemies around you (I haven't tested this yet). If so, that would likely set it one notch above Steel Sybil's single-target heavy attack. Also, the Guillotine is easily targetable this season in Umbral Engrams. Steel Sybil has been around for a while and you might already have that god roll. If not, Steel Sybil is also reissued this season in the world loot pool so you may get a good roll there. Whichever sword you run, slap a Boss Spec mod on it to do another multiplicative 7.77% damage (not a joke - tested that in the Tribute Hall yesterday).
Build and Mod Discussion
Source: Season 11 activity / prismatic recaster
Arc mod, costs 4 energy, slots into the seasonal mod slot of any armor.
"While Charged with Light, dealing damage with a Sword gives you bonus damage for 5 seconds, consuming one stack of Charged with Light."
"Secondary Perk: When at least one other Arc mod is socketed into this armor, Lucent Blade greatly increases the charge rate for your equipped swords."
This is the cornerstone of the build - giving the player big DPS buffs on bosses. This spends stacks of CwL to give a 35% damage buff, which stacks with the Whirlwind Blade perk on swords as well as Boss Spec weapon mods and any source of debuff on the enemy you're damaging. When procced, you'll get a buff "Keened" which lasts for 5 seconds and gives you the damage bonus. While Keened is active, you won't consume additional stacks of Charged with Light (I tested this), so go ahead and whack away with abandon at your target. One stack at a time will get consumed to keep this going if your DPS lasts for more than 5 seconds.
Source: Season 11 activity / prismatic recaster
Arc mod, costs 5 energy, slots into the seasonal mod slot of any armor.
"Become Charged with Light by rapidly defeating combatants with Pulse Rifles, Sidearms, or Submachine Guns."
"Secondary perk: When at least one other Arc mod is socketed into this armor, defeating combatants with a Pulse Rifle grants a chance to drop Special ammo for your allies."
Swift Charge is one of the two ways we'll earn stacks of CwL. You'll want to spam your Recluse to get stacks while simultaneously proccing Nez Sin's perk to improve your ability regeneration. You can also earn CwL with your kinetic pulse rifle, but that won't help with Nez Sin, and you won't be killing mobs nearly as quickly. The secondary perk might be helpful if you're doing content with a fireteam, but it doesn't directly benefit you. My armor mod recommendations include the basic arc "Sword Scavenger" mod in order to enable this secondary perk, but you could forego it and just use another mod if you wish. You could use a second Enhanced Sword Scavenger from the artifact, but in testing the build I had lots of sword ammo already. You might use that two energy to put into the general mod slot on your legs and make that another Discipline mod - up to you.
UPDATE: If you're using Gnawing Hunger instead of Recluse, you should change Swift Charge to Sustained Charge - it does the same thing but for auto rifles. Sourced from the prismatic recaster. Solar mod, costs 4 energy, slots into the seasonal mod slot of any armor. "Become Charged with Light by rapidly defeating combatants with Auto Rifles, Trace Rifles, or Machine Guns."