Thiem had just won the week before in Buenos Aires. Nadal has lost early in the clay season as well, so not exactly sold that one match in Rio means Thiem is in decline when his stats are still improving. You do realize that Thiem would have won a whole lot on clay last year if Nadal had not been in his way?
The field is young. Thiem is getting stronger in the stamina department year by year. I'd definitely rate Thiem and Zverev much more highly than Wawrinka and Murray at the same age. I might even rate them higher than peak Murray and Wawa, since Zverev is undefeated against Wawa and Djoko. Thiem has beaten Wawrinka on clay and Murray as well. Murray appears to not match up that well with Thiem on any surface would be my guess. Despite a clear matchup issue with Nadal, Zverev is still excellent on clay.
I hope Delpo does well on clay this year, but I expect you're going to be in for a rude awakening this year. People mistake weak field right now on clay because all the geriatric pigeons are dead meat on clay. With all the youth coming up the clay field looks very secure for years to come.
Lets face reality, if Bjorn Borg was trying to come up against Nadal he probably would have had a stinted career due to the constant bruising of his ego. The guy retired as soon as he had any whiff of competition for #1. Don't think he would have enjoyed being 2nd fiddle to Nadal or even Peakovic for that matter. The clay field is loaded with young talent right now if you remove Nadal from the picture.