Please, just give users the ability to say whether they want this "extra safety" control on. (If it even is extra safety, but whatever.)
If they don't, they can sideload, and use F-Droid, and etc.
And then we can debate whether it should be default on, or default off, and how hard it should be to turn off.
I agree, but it is not good enough. They should also need to actually check for malware and other problems with their own app store, in addition to allowing loading your own unverified (or that you verify yourself in a different way) software if you want to do too (perhaps with the option to configure this, as you mentioned).
(I do not use iPhone nor Android and I won't, even if they do fix these problems.)