I don't think comparing a 39 year old Frank Thomas to his 22 year old self is the same as comparing 18/19 year old Vladdy to 21 year old Vladdy lol. The former's hitting ability declining is just a natural product of age based decline. Vlad got fat, beyond reasonable body growth given his age, and his batted ball profile got bad. It's not comparable at all lol.
Frank Thomas didn't even get fat, he was just an absolute tank his whole career and obviously at some point his bat speed was gonna decline.