UAC is even more useless, it just tells you "Do you want to allow xyz to make changes to your computer", without telling you what any of those changes or permissions are. Android permission prompts are way better.
The UAC prompt is essentially "sudo" - it grants root to whatever program is running. You really can't really implement a more granular permissions system without significant engineering effort, because you need to ensure that granting one permission doesn't result in privilege escalation. For instance, granting permissions to modify Program Files/Windows directory can be abused to get steal permissions from other applications, by replacing existing executables with malicious ones.
>Android permission prompts are way better.
Not really comparable because "regular" Windows programs aren't sandboxed. So they kinda already all the android "permissions" already (eg. contacts - they can simply read off disk). A better comparison would be root, which essentially has the same ux as Windows UAC.