Makes sense, but I am not sure if the trade off is that much. In the PlayStore, you have to TRUST Google to not fuck around in first-time installs. There is no first install check in the PlayStore as well for those attack vectors.
Have you heard of https://github.com/soupslurpr/AppVerifier ?
It's at least an attempt to have a sort of community run trusted attested developer keyring. Obtainium was considering some kind of integration
Like I said, trusting Google/Fdroid to attest first time installs is arguably better (securitywise) than expecting common users to attest each app vendor individually.