Okay, but sideloading is worse? AFAICT the problem we're discussing was in F-Droid doing extra verification (somewhat incorrectly, apparently) of an APK before handing it to Android to install. Regardless of F-Droid, Android will check signatures on updates against the installed version. So your response to F-Droid imperfectly checking signatures as an extra verification on first install... is to skip that entirely and do zero verification on first install? That's strictly worse for your security.