Not every single of them, but the guys from 90s are way too big (with technique I should add, before the Willard remark)
I hear you. But Seldon had no chin and if nothing else Dempsey could punch and was tenacious. Seldon wasn't a big puncher either and so I don't necessarily see him stopping Dempsey regardless of the fact that he was bigger.
Seldon wasn't a huge puncher but he did score 36 KOs in 40 wins. Often due accumulation and not against the best opposition but nevertheless, he had some pop. Dempsey was hurt (according to reports, I have not seen the Brennan fight on tape) against likes of Charpentier (172 lbs), Brennan and Tunney and knocked out by Firpo, so Dempsey could be hit and hurt. Also, Dempsey always struggled with moving, technical boxers, so I can't see him finding Seldon in time.