You keep bringing up this thing about Harrison, which as far comparisons go, is apples-to-geodes. I also don't think that Harrison should be allowed 10 minutes off the court to change clothes, but that's neither here nor there. Nothing to do with the MTO rule, but simply exists as an immediate and disingenuous point of whataboutery.
And it's really not. It's not saying that if you get injured or seriously aggravate something mid-match, you shouldn't get treatment (I'm pretty sure the determination is left to the on-site physio, and not the supervisor); it's saying if your injury is serious enough before entering a tournament or match that it requires you to need an MTO, then perhaps you shouldn't play. Maybe it will encourage players to be more cautious about their bodies, and maybe it will stop wasting fans and other players' time when guys are taking MTOs throughout a tourney's entirety.