For discussion purposes here is Treantmonks brief analysis of Pact of the Blade, for discussion purposes. Sorry if I miss something, and I will add Kurotowa's doubts here too:
He did his usual assessment set to 13th level. The level is arbitrary but it's held consistent for his analysis for each class/subclass as a simple test case comparison so he can put them all on one chart. He's not claiming it's completely fair or representative, just a simple test to sort of hold his finger in the air initially. Once they settle on stuff he does a much deeper dive at multiple levels and varies his assumptions.
His quick sample build, not fully optimized.
Species: Any, +2 Chr, +1 Con,
Stats: Str 13, Dex 14, Con 14, Int 8, Wis 8, Chr 17
Notes: Melee Heavy weapons requires a 13 str (Greatsword), Ranged heavy weapon requires 13 dex (Longbow. assumes magic unbonused one at 13th level I think)
First lev feat: Lightly armored (gives medium armor prof for half-plate)
4th lev ASI: Warcaster, chr now 18
8th lev ASI: Charisma +2 for chr 20
12th lev ASI: great weapon master [ Note: Kurotowa disputes they can access GWM due to only temporary Martial Weapon Proficiency ]
Invocations (8 of them): Pact of the Blade (Chr for attack and damage rolls, modify damage types, create weapon as bonus action);
Thirsting Blade (3 attacks with attack action; Lifedrinker (+1d6 damage and healing option); Eldritch smite (used for Crits, 12d8 extra damage on a crit); Otherworldly Leap (20 feet extra movement); three more invocations as you see fit (Agonizing and Repelling blast? Lessons of the First Ones for Tough or Alert? Whatever).
Melee: Greatsword: Graze Mastery, deliver Charisma Mod damage on a miss (5), Base Weapon Damage: 2d6,
Rd 1 Bonus Action, spend 1 of 3 pact slots on Spirit Shroud (5th lev) = +2d8 additional damage to attacks, 1 minute.
Close to Melee. Assuming 60% chance to hit:
Attack #1:
2d6+5 Base Weapon Damage
1d6 Lifedrinker
2d8 Sprit Shroud [Note: Kurotowa disputes Spirit Shroud up 100% of the time and, I assume, thinks this should be reduces by some percentage it's assumed it would be down due to a failed concentration save I assume]
24.5 Average Damage on a Hit
60% chance to hit x 24.5= 14.7 average
40% chance to miss (Graze) x 5 = 2 average
5% chance to Crit x 73.5 Damage for Crits (Eldritch Smite used on Crits) = 3.68 average [Note: Kurotowa disputes the assumption a spell slot will always be available to boost the crit damage here and this estimate should be reduced to reflect a more realistic number of times such a spell slot will be available]
Attack #1 total average damage: 20.38
Attack # 2: 20.38 average damage
Attack #3: 20.38 average damage
Great Weapon Master (Applies proficiency bonus to damage once per round): Chance of hitting at least once with 3 attacks = 94% x 5 (proficiency bonus) = 4.7 damage average per round.
Total Damage Per Round: 65. 84 average (20.38 + 20.38 + 20.38 + 4.7)
Reference: Berserker Barbarian, Beast Master Ranger, Champion Fighter, Assassin Rogue, and Devotion Paladin are all doing around 28 damage per round at this level. 147% over "baseline" which is a Warlock using Eldritch Blast with Agonizing Blast and Hex.
Ranged: Longbow (moontouched or whatever, assumes no magic bonus to hit and damage just base 1d8+5 damage). Includes Slow Mastery, which is nice but not changing DPR calculation.
Rd 1 Bonus Action: Hex (same as baseline attack)
Attack #1 1d8+5
1d6 Lifedrinker
1d6 Hex
Total average damage for a hit = 16.5
60% chance to hit = 9.9 average damage
5% chance to crit (Eldritch Smite used on Crits) 89.5 damage on crit = 4.48 average [BUT SEE BELOW]
Attack #1 total average damage: 14.38
Attack #2 total average damage: 14.38
Attack #3 total average damage: 14.38
Great Weapon Master (Applies proficiency bonus to damage once per round - and yes, it now applies to a longbow too): Chance of hitting at least once with 3 attacks = 94% x 5 (proficiency bonus) = 4.7 damage average per round.
Total Damage Per Round: 47.84 average (14.38 + 14.38 + 14.38 + 4.7), which is 79% more than Eldritch Blast with Agonizing Blast and Hex.
Now Eldritch Smite can use more spell slots. So lets assume for this one you never took Eldritch Smite and that big boost on crits goes away. Crits are now 5% x 12.5 = 0.63. New total is 36.59, which is still 37% more than Eldritch Blast + Agonizing Blast + Hex. And you're Slowing Target (Weapon Mastery) rather than pushing Target (Repelling Blast). And getting more range from longbow than Eldritch Blast. Bottom Line: why use Eldritch Blast anymore when this does a lot more damage for just one more invocation involved really?
He concludes with this about this build"
1. Pact of the Blade Warlocks Outdamage all other tested classes by a lot
2. Has Switchable Damage Types (four, changeable each attack)
3. Has it's bonus action available most rounds beyond first
4. Has faster movement, same speed as same level monk
5. Has three more invocation options left to choose (Lessons of the First Ones to access feats without pre-requisites so can get something like Tough to get HP close to barbarians, Lucky, Alert to win initiative, etc.)
6. Can switch between melee and ranged easily with one bonus action
7. Can access every weapon mastery with bonus action (which is better than fighters get - can just switch to Topple or Push or Graze each round)
8. Has in combat no-action healing (Lifedrinker)
9. Still has spells (will eventually get 9th level spells)
And all this he didn't even add in extra attacks from heavy weapon master, or any subclass boosts like from Genie,.
His quick recommendations:
Lifedrinker should require level 11
Thirsting Blade shouldn't scale at level 11
I think it's implied, but he doesn't state it, that maybe this is too many weapon attacks per round with weapons for a spellcasting class?
I also think we could re-do this assuming 100% of Kurotowa's doubts are applied. So probably assume Spirit Shroud is down 20% of the time, assume 3 battles between short rests instead of 2 so reduce the boosted crit such that 1/3 of it would be only a non-boosted crit (?), and assume no GWM but another feat?
I am still betting the numbers come out so far ahead of any other class it still raises an eyebrow of concern.
