tac I'm not sure if I fully follow the principal argument, since on Android anyone can download and install an APK from anywhere if the system allows it, so by that logic it would follow that browsers and file managers should also be excluded as they can enable installing APKs from the Internet and/or the local filesystem.
For an app store to function, it needs permission to install other apps.
Your browser might be able to download an app, but the act of downloading it does not make it immediately installed.
I actually usually use my browser to download new apps unavailable through Accrescent through my browser, so I can have a chance to verify them manually before the first install; only Obtainium allows this AFAIK, other app stores won't necessarily even keep the downloaded APKs in a user accessible location to verify after cancelling the first install.
Accrescent tries to ensure the apps you download are genuine, and that they adhere to some basic rules regarding their functionality.
This combination means that as long as Accrescent itself is implemented correctly, an app you've downloaded from it is fairly safe to use, as long as the developer of said app isn't abusing some exploit in a malicious way.
Accrescent is available through the GrapheneOS app store, which means an ordinary user of GOS might install it and assume an app store installed through it would itself adhere to these principles.
Accrescent, AFAICT, does not aim to be a curated app store containing only the most high quality apps, but rather a general secure app store, which in contrast to existing solutions does not require harming your privacy as much; adding other app stores, regardless of the previous points, can only slow adoption of Accrescent IMO, as there will be a smaller incentive for developers to add their apps to it.