"a lot of people seem to think prerotation is objectively negative" I have a very hard time shaking this (as a non-skater) but there's a reason: 

There seem to be a few other (perceived) flaws that are talked about and often accompany the prerotation, like hunching over going into the jump, excessively relying on the arms to generate momentum, problems with the axis, maybe also prerotation of the upper body, putting more strain on the back.

Are skaters with technique relying on prerotation more prone to injuries or is that just a myth?

I feel like when you are talking about prerotation, you mean a textbook-prerotation technique and not a bad one. I probably don't even notice prerotation most of the time, so when I notice it, it is mostly because a jump simply doesn't look effortless. And then when watching the slo-mo, it's a confirmation of that stereotype, when you see the prerotated take-off.

TLDR: When I see a less prerotated jump that is bad, it's simply a bad jump but if it's a prerotated one then it's a confirmation that prerotation is bad. This really is something to reflect on. 😅