I am no specialist, just someone who avoided plenty of brands. My theorie is that they lock down some stock apps so it doesn't look so fishy when Facebook and co is locked too to get good ad deals.

Every phone I owned in the last 10 years allowed full control about apps without root. That's a nexus, a cheap Oppo and now a Xiaomi.

Edit:// I thought you need an account to activate the iphone? Not sure if I am totally wrong