Primordial Warlock

Doesn't seem inherently villainous to me.  You could easily use it to make a character like Elsa, from the Frozen franchise.  Last I checked, she's not a villain.

So far only 2 of villainous subclasses seem villainous. Hell Knight fighter and Pestilence cleric. The rest aren’t inherently villainous.

Very few options could be inherently villainous. Just like how very few are inherently heroic (there’s devotion paladin I guess, but much beyond that any of them can be a bad guy). It’s never about the tools, it’s about how you use them. It will come down to role play choices.
These subclasses do, however, seem to give an easier path to be a villain, or at least an anti-hero.