Kinematics
Hero
Forgot to list Agonizing Blast in the list. Fixed.You've given Pact of the Blade one more invocation than you've given Eldritch Blast in your analysis, so yes, of course the results are going to be uneven.
And yes, they don't have the same number of invocations because there were no other invocations to affect Eldritch Blast's damage. Feel free to use whatever you want to balance that out.
I already made exactly that argument earlier in the thread. This post was specifically to address your false claims that there's a negligible (~3 point) difference in damage between the EB setup and the PoB setup.That's a great argument for changing Spirit Shroud's upcast benefit, not for nerfing thirsting blade.
The problem is not any single ability, but the combination of several factors, one of which is Thirsting Blade. Saying that Thirsting Blade is "not broken" is rather missing the point. The PoB setup can be brought back down to "midline" levels in several different ways. The question is, how many different things are the designers willing to change to make that happen?None of this suggests to me that there's a problem with thirsting blade.
Removing the third attack from Thirsting Blade cuts off the damage amplification of the damage boosting effects (Hex/Shroud/Lifedrinker), and any potential spells or multiclass effects added later. Removing the damage scaling of Spirit Shroud makes it a minor boost over Hex, and not so excessive. Or you could remove it altogether*. Lifedrinker doesn't need to add extra damage, and can just heal you when you attack. You could remove heavy weapons from the available weapons Pact of the Blade grants proficiency in.
* I'm not sure how easy it is to entirely remove a spell, since in theory you should be able to use older books, which means Spirit Shroud is always hanging out there in Tasha's.
The combo is definitely overpowered, and it definitely needs to be nerfed, but there are several approaches for how to do so. Any of those changes could be done (though only one or two should be needed; definitely not all of them), but we don't know what the design goals of WotC are in this matter.