Both. Vaughn has never had one season as good as any of those first basemen you listed. The only reason your comparison works is because most of those guys are old and/or on the downside of their careers. Tellez isn’t old but he was never really a good player to begin with, just like Vaughn.
If we have to contemplate whether our 26 year old former #3 overall 1B pick is worth $6 million or not, the story has already been written. I guess the fact that he is starting at 1B in the MLB is proof that he isn’t some sort of colossal bust, but then again, he should probably be a bench player.