So I went to PGCC and played a bit with Harbingers. I have mostly changed my opinion and think they are probably fine. I do have a few key notes. These were mostly taken from a 2-h EDR build's perspective, as that is what my Hexblade on live is, so I was looking at how that would look after the update.
Cursed Razor is the worst of the paths, and I think it is by a large margin.
The effects on atrocities are worse, Dark Seraph's either daze or stun, which is huge. Crimson Counts have extra damage on melee. By comparison, a slow, a teleport and entangle is not amazing.
They also have the worse killing claimed creature effect. 11/+6 DR (Crimson) and +2AB (Dark Serapth) are far better than +2AC.
They also have the worse weapon hex. Crimson and Dark Seraph have 1d6/2d4/2d6 and Cursed Razor has 1d4+1d4/1d6+1d6/1d8+1d8. Assuming 5/- resistances, Crimson and Dark Seraph are looking at 2.5 on average, and Cursed Razor at 0. If you look at ranges, Crimson and Dark Seraph are looking at 0-7 damage and Cursed Razor 0-3 + 0-3. It is plain worse. Their Dark claim increases vulnerability to their types but I don't think this is great, other Dark claims have better effects. Cold is also a bad type as a lot of subraces and spell provide immunity or DI against cold. Entropy and Bleed are harder to come by.
The Killing a claimed creature with any Atrocity ability mechanic is clunky.
These are big bonus which are really hard to get. In PvE they are fine, you will be able to eventually get them every 2 turns. But for PvP these will likely not be there. A way to get around this is to summon creature 1, Dark claim and use atrocity on them to get the bonus instantly, then you only have 26 seconds until you can claim your PvP target, which I think we can all agree is just a silly way to circumvent mechanics. Going to PvP without 11/+6 DR or without the extra +2 AB is absolutely huge.
I don't have a suggestion on how to make it less clunky, maybe reduce the bonus but make it easier to attain.
Blood Homunculus and Black Blade of Disaster
One is a bit too weak, the other is a tad too strong.
Blood Homunculus AB is just way too low, at level 30 Harbinger I was looking at 33 AB, it did have a lot of HP and immunities, so maybe this is currently more of a PvE sponge? In PvP it can just be ignored.
Black Blade of Disaster (with the Improved Weapon Hex had +45 AB (which may be on the higher side), dealing 2d6 + 34 (15-20x2).
The blade still has the on-hit save or die, this should absolutely be removed.
The blade is entirely immune to physical or elemental damage (did not try magical). I assume mords just removes it. This makes the interaction very binary, it either has an amazing staying power, or just none at all.
I am still not over Mortality Undone nerfing their DI from Hexblade from 18% down to 10%. I would ask if this could be bumped to older values for Harbingers with a hard CON of 19 (basically the EDR builds, or maybe for 2H builds as these are missing the 10% Piercing DI from using a shield too). These will never be mechanically optimal. Right now you are better running sword and shield, going higher on Strength for more AB, specially with easier access to Divine Might and Divine Shield due to Divine Patronage.
Edit: the Blade of Disaster AB is actually +40, the character sheet is lying for some reason. I would say it should probably gain 3 AB and lose the on-hit kill.