He might have, yes. On the other hand, Nadal was very erratic at the time. He would have had Murray and Wawrinka in the semi final and final, Murray having beaten Nadal at 2015 Madrid and Wawrinka having beaten Nadal at 2015 Rome, but over best of 5 sets at Roland Garros who knows? It's similar to Muster at the 1997 French Open in a way. Muster had a poor clay season in 1997, but had he beaten Kuerten in the third round, I think Muster might have won the whole tournament. His opponents would have been Medvedev, Kafelnikov, Dewulf and Bruguera. Muster has an excellent record against 3 of those, and would likely have had more trouble with the lower ranked Dewulf ironically.
Nadal's best is 2008 French Open good. Nadal was playing pretty well at the 2021 French Open, but don't go overboard. He had just won the 2021 Italian Open, where he beat Djokovic in the final. Nadal could have won the 2021 French Open, and I think he would have had he taken his set point in the third set against Djokovic, but it wasn't to be. Nadal had unfinished business with Tsitsipas had that been the final.
Nadal did have a foot injury at the 2021 French Open, but he also did at the 2022 French Open as well, and he beat Djokovic at the latter.