It's trying to do that. Unless I'm misunderstanding what it's displaying in the video (which is what happens every time), but it seems to me 'UE4 prerequisites setup' would be exactly what you're telling me should fix it. Instead it becomes a forever loop. If you haven't watched the whole video I posted in my original post, please do. As soon as the video ends, it's basically just rinse and repeat. I do the weird uninstalling the prerequisites it prompts? That error. I install it via the same process? That error. I try to open again and am prompted to uninstall the UE4 again.

Launching it from the install files worked! Frustrating that the itch launcher is botching it but it does work! Much appreciated

I wonder how itch.io launcher messes up applications, instead of launch them, you download the same thing anyway, rendering it useless.