Well if the app is on a different store you wouldn't be able to currently install it all, right? So you have only expanded your options and it's up to you if you choose to exercise them or not.
Well, the app might be currently available in the AppStore but would now be able to move to an AltStore. Plenty of apps I bought in the past have been pulled from macOS AppStore but are available on websites.
In the past I even had banks and even the public sector offices abusing Windows and macOS security and forcing me to install the equivalent of a rootkit in my computer. Without a sufficiently smart sandbox I bet this problem will come back.
On the other hand, that doesn't seem to have happened on Android, at least not in a wide scale.
