Thiem has been going downhill since Roland Garros.Who knows if it will ever happen. Each slam seems like the last. He is getting older and his once famed mental strength is no longer what it used to be. Nor is his physicality.
Plus he lacks belief against Novak and Fed. And these other next gen guys are finally going to get better.
Will there be another slam where conditions line up as they did in the UsOpen? Will Nadal be able to overcome a stronger Thiem and Djokovic in Paris?
Big questions, but no easy answers.
And Djokovic has been going downhill on clay for awhile.
And don't even make me laugh mentioning Federer at Roland Garros at this point.
We will see if Medvedev is a capable clay court contender or not.
You do make valid points on his chances for non RG slams but he could easily get there just on RG alone. As for the other slams what keeps happening will probably happen again, that he avoids Djokovic (and maybe Federer) who both seem more prone to being taken out by the field ATM than Nadal (especialy Federer) to win again.