Is Gene Tunney’s win over Jack Dempsey more impressive than Fury’s over Wlad. Wlad was 39 but still very active fighting twice a year. Jack was only 31 but had not had a pro fight in 3 years. Both men were viewed as pretty invincible at the time these men turned the trick on them. Both champions although faded (badly) turned in rather strong efforts in their next Bouts - Dempsey in a grueling controversial win over Jack Sharkey and Wlad in a grueling epic loss to Joshua.
What’s impressive for Gene that Fury didn’t do but I didn’t factor it into the original question is that Gene turned the trick twice. Shame Fury didn’t afford Wlad the opportunity to try and retain title.