No, the problem here is that DRM systems require you have an account with an entity that can terminate your account without refunding you for all the purchases

No, the problem here is that DRM systems require you have an account with an entity that can terminate your account without refunding you for all the purchases that are tied to the account. This is true for any DRM system. A 3rd party App Store would just mean you have a different company that can close your account and disable products you already paid for.