It's interesting how Thiem was streaky overall but fairly consistent at the French for an extended period. His loss to Schwartzman could easily be chalked up to mental fatigue. Agassi was just never as consistent. Obviously this is pure opinion backed by hypothetical comparison, I mean Agassi only faced Nadal twice both on hard in his twilight so we have literally nothing to go on with Thiem. But your question of Ferrer is intriguing enough but he only won a single set in 4 matches, so in that sense Thiem is above him.
Ah you preach about those AO runs don't you? Well you can have them, are they in any way worse than Nadal 2017-2019? Oh yes, DANIIIIIIIIL get out of here. Also can't forget Andre skipping AOs in his prime which Nadal did once I guess?
My reasoning:
1. Federer didn't drop a set which is rarer at USO and with a harder draw, that WImbledon draw was garbage.
2. Federer was mentally clean that tournament and should have beat Delpo in 4, Nadal had little in his way and lost a grinder match
3. Novak coming back from 0-2, double MP in semis and railed Nadal in the final, Rafa should have lost to Fed at the French and got taken to 5 by Isner.
4. Nadal USO Series Triple Crown, Fed pushed hard by 35 year old Agassi for 3 sets.
5. Roddick just the better player, 7-9 Slams without Fed alone.
6. Fed nearly lost to Baghdatis, has cramps to thank for the win, Novak wins epic 5 setter on route.
7. Well that Novak beat clean Fed in the final, Fed lost a match he should have won against a lesser opponent on that surface.
