what can’t I get in the Play store that I actually want

Well, for starters, versions of apps without Google play store tracking. Or without GMS/Firebase so the apps aren’t constantly being awakened whenever someone else decides.

Or old apps that Google has decided you don’t need anymore because they “won’t run” on current versions of Android, yet work fine.

Or, any app category that Google doesn’t permit you to publish to play, like my system wide ad blockers.

Or apps that aren’t malware, since Play store is the single greatest source of malware.