You can ask any rock or metal singer about 80's and even early 90's Sammy and what he did on those albums performance wise. Those performances are out of this world and if you don't realize that when you listen to them you simply have no idea about it. He is superhuman on some of that shit, and its not just about his range. Lyrically I would agree he is nothing special. Especially when he was trying to write "raunchy" lyrics they're cringy. You can tell Sammy is not that guy while Dave is a very believable lecherous pervert.
Seriously. Roth is probably the worst singer to ever have such talented players around him. It's actually pretty funny to think of how little ability and talent he had with Eddie, Vai, and Becker ostensibly backing him up during his career. Ostensibly only because at least in Eddie's case, he was almost equally fronting the band. Maybe aside from nostalgia that's the other reason some guitarists are so militantly anti anything but Roth era VH - when Roth was in, the guitar essentially always overshadowed the vocal. The vocal was necessary but more of an accompaniment to the instrumental.