I don't think there's been an "evolution" at SS.
The ability to handle SS defensively has always been the minimum bar, and there aren't a lot of humans capable. From there, SS's who can hit well were, and are, hard to find.
But there's always been a few. Honus Wagner, Joe Cronin, Lou Boudreau, Ernoe Banks, Luke Appling, Arky Vaughn, just to name a few.
There's just never been very many, and there still aren't.
Gonna have to disagree with this "today's teams are so much better" theory as well. The Big Red Machine would be The Big Red Machine today.