2 - Manual installation methods can be insecure because a lot of people don't update their apps all the time. Obviously rooting a phone is insecure, but having no auto updates in 2023 is crazy.
4 - It is very true, having zero quality control on new apps. The flagging of apps with problems is just following the FOSS philosophy. Any FOSS app can be added to F-Droid.
5 - Not sure why you would want to install abandoned apps on F-Droid, let alone use an EOL device. A lot of people don't check if apps are maintained because they trust their app store.
6 - FOSS doesn't automatically mean its secure or private. Also, why is it that I have to install proprietary apps only on the Google Play Store?
7 - FDroid signing keys isn't an advantage because it requires an extra layer of trust. I'm already trusting the developer by installing their app, so the developer should be signing the keys. This is a reason why Signal is not on F-Droid.
I think your thinking im against FOSS but you're not understanding. Many people in the FOSS community only care about privacy and ignore security. A developer can implement security benefits to FOSS but many people don't care to do it.
Accrescent is FOSS and it has much higher security benefits than F-Droid. Accrescent allows both open and closed sourced apps because there's no benefit being exclusive to having FOSS apps in their catalog.
If the user chooses to not use proprietary apps on Accrescent, they don't have to install them.