If Chrome was allowed on iOS be sure Google would dump unlimited money to get people to use it. Websites would further go down the path of only testing on Chrome, and Google would continue stuffing their browser full of oftentimes needless features. And they’d continue all their other disgusting practices like AMP even less fettered than before.
The literal only hedge against this right now is Safari. I thank the powers that be that Apple doesn’t let other engines on.
That, and, Safari is miles ahead of any other engine in terms of performance. It’s not even close.
And answer this: how would allowing other engines increase privacy? WebKit does more for privacy than almost any other, and allows installing privacy extensions and wrappers like Firefox. Without that, you’d have people using Chrome more than using Firefox.. a regression in privacy.