Vader definitely needs a buff. As others have said speed one on a melee unit is a serious handicap, although I’d retain it as it fits the character.
I accept that any unit can be run and that it’s periodically possible to do great things with even the most underwhelming of units, but that doesn’t mean underwhelming units don’t deserve to be improved so that they’re more consistently useful (and played more often).
I think the aim should be to have every unit in the game seeing similar usage to other comparable units. I doubt it’s possible to ever truly achieve this but it’s worth having as an aim.
For buffing Vader, there’re a number of ways it could be done. Personally I’d like to see his unit card revised to better match the essence of the character. To do this I’d consider what the prominent traits of the character are and then incorporate them onto his card. I think his essential traits could be distilled down to: slow, extremely hard to kill, terrifying, and likes force choking people. With those things in mind you could revisit commander Vader’s unit card and retain speed 1, add surge to defence, add demoralize 2, and fold the effect of Force Choke onto his unit card as a free action. That would make an improved and thematic version of the character.
Alternatively you could just continue to drop his points cost or remove Relentless and give him a free attack action instead (to expand the options of his action economy and allow him to double move, Force Push enemies into melee with himself and then attack them - thereby extending his melee threat range) These aren’t as thematic but any buff would be welcome.