Can you be more specific on how iOS blocks other browsers? You mean for embedded browser engine in apps?
I would bet Google's track record would easily allow them to defend this in court. More an issue with Google though.
And the problem isn't abstract. Safari lacks a ton of very useful API implementations. Like, try programming a QMK keyboard on an iPhone: it's literally the only platform in the whole world unable to run the Via web app.
The security angle is easy to understand.
Not sure why Apple cares about control.
But it easier just to want to make Apple seem bad, so there's that.