Players are all a product of the environment they are brought up in, so this makes no sense to compare previous gen 30 yr olds and see if they will win CYGS now or not.
Sending Federer 2015 to 2021 and expecting he won't win AO is silly, because it doesn't work that way, the 33-34 yr old Fed playing in 2021 would be different from the 1981 born you found in 2015, the injury patterns, peak levels will all vary, his level vs Nadal, his H2H all might also vary, we might find Federer win 2 french opens after 28 when Nadal's footspeed declined considerably or was injured, we might Fed with more confidence in the absence of a Novak to tackle, his injury patterns would change, lot of things will vary, his body structure might also vary.
Can you send a 30 yr old Sampras of 2001 to 2021 and expect him to win ? Nope
But what if Sampras was born in 1991 and then was 30 yrs old in 2021 ? Would you bet against him? He could definetly win as he would be a different player, having modern day fitness into the 30s, a different game with better baselining skills.....
So it is pointless to compare prev gen 30 yrs olds, even Fed makes no sense, a lot can change with 6 years of birth. It is like a child starting to play with a certain type of racquet or be subjected to a certain type of training from age 10 and another from 16, makes a big difference....... Most hypotheticals in TTW are total trash because people just bring a player from 1 year to the present to play, that is not the way to compare players, the BUTTERFLY EFFECT has to be taken into account.