Well, you don't need to speculate, we know it to be true. JT literally just spent 9 days out, so he should have gone on the IL and almost certainly would have missed longer in a normal season. Harper maybe plays through this with 2-3 days off in a normal season, or maybe he goes on the IL for two weeks or two months or the rest of the season.
And it's not so much the condensed season as the specific condensed Phillies season. The unexpected time off delayed the wear and tear and then the doubleheaders and reduced off days made rest even harder. I don't think Joe pushed them too much though. He gave guys days off. He rotated the DH days. Percentage-wise nobody made as many starts in the field as they would have in a normal season. And how many game threads started with "why is so-and-so starting today?," as always whenever a starter rests.
In a normal season they also maybe don't all happen at the same time. If memory serves JT finished last season hurt too. And of course Cutch was long gone, and Bruce was less healthy than he is now, and even Haseley spent some time on the IL (along with Quinn as usual).
Definitely true about the depth. Of course if we had a bullpen we'd just be dropping from first in the divison to second place, not battling for last wild card.