Not close to 80kg but Olano, Zülle, Ullrich, Armstrong, Riis were all above 70kg. Not crazy but definitely above the norm compared to today (even Dumoulin at his peak was less than 70kg). I think the surrounding factors regarding TT relevance
@Libertine Seguros mentioned definitely played a role but EPO must have had an impact as well on helping the bigger guys. Ullrich really shouldn't have the best non-Pantani, non-ITT time up Alpe d'Huez or the Madeleine or Arcalis record, Riis not the Hautacam record, Indurain not the La Plagne record...
An other random thing I noted re-watching a lot of 90s videos is the insane amount of time people are climbing out of the saddle. Watch the Pantani one man show in the Giro 98 or 99 and he's basically running up the mountain, not just accelerations, constant tempo pushing. I wonder if this is gear related or has also some physiological EPO background.