

I believe it was canonized that Vader made improvements when it was required. Vader was still a technical genius and a pilot that no one rivaled.
Take his right hand for instance - he was given the first prosthetic, that he replaced during the clone wars. One of his legs in a comic gets beat to all hell, and he rips off a jedi training droid leg to replace it, which works better and is far sturdier.
But originally it was intended to be a hinderance. Anikin was a walking vergence in the force, simply by existing he made his connection to the force stronger. By sticking him in a much less technically advanced cyborg suit than what Grievous got, he could also just blast him with some lightning to weaken him physically again.
Spain? Read the room.