I have the iPhone since the first generations and I used to root it and install the other app store.
Decades after I use my phone for online banking and I heavily trust the security pf the iPhones despite some malwares here and there. Android sucks with security and I would not want Apple to handle increased security for having multiple stores in its phone.
Apple products is good for me because they focus on unity: its own hardware, its own OS, its own App store. This is where quality comes from. If you want another store, use Android.