If a company offers some benefit at the cost of some restriction, then users should decide if that benefit is worth the cost. For most Android users, it will be - my grandma isn't interested in the freedom of indie devs to develop for her phone, she's interested in not accidentally installing malware.
I don't like that as much as you don't - for my own devices. But like anyone else who cares about that, I can root it and get past the digital nanny state.
Owner having full control over the device does not prevent a company to offer same benefits and restrictions. But these restrictions need to be optional, so the owner can decide whether to enable or disable them.
A few years ago "A smartphone so intuitive that grandma can understand it." used to literally be one of the arguments cited for picking iOS over Android. The UX is far more polished and you are far more likely to find an interesting iOS-exclusive app than an Android-exclusive.
Further, as a hardware manufacturer, Apple is far more likely to manage its walled garden in the consumer's interest, as compared to Google - an advertising company.
If Android gets locked up, all the high-end Android manufacturers, especially Samsung, are going to face a slow, but inevitable death.