fdroid sucks, but not for those reasons. How about it uses fdroids signing key, unlike obtainium, which uses the developer's signing key.

I'm all for a store that only allows FOSS apps, but I don't like how they use their own signing keys. That's definitely suspicious.

Fdroid is also extremely insecure:

F-Droid Security Issues

F-Droid is a popular alternative app repository for Android, especially known for its main repository dedicated to free and open-source software. F...

most important apps are signed by fdroid, not by the app devs (for the most part at least; fdroid offers a method to build the app in a way that permit devs to sign themself, but pratically noone uses it cause require much work). So if someone compromise fdroid, he can put arbitrary malware in the update of all your fdroid apps.

I mainly use Obtainium and Github release urls. Some apps are unforunately only available via Fdroid.