Can't you just check the network activity at the OS level to get an idea of which is more private? This can be done when evaluating browsers and other apps. For instance, Chrome and Edge are constantly sending data back to Google and MS. You don't know specifically what is being sent but it is pretty obvious what is happening. You can see this in every application they make. Safari in comparison sends fairly little telemetry data back to Apple. There are other browsers that send no telemetry at all so those in theory should be the most private. And then you can look at how each company does business in general. Looking at ublock origin I can see the web is full of trackers from Google, MS, facebook, twitter, tiktok, etc, but I don't see Apple trackers being blocked. Because those other companies are fundamentally in the business of spying and surveillance capitalism. The "products" they make are the means by which they do so. Apple OTOH is fundamentally in the business of selling devices and other hardware.
Whenever this topic comes up, I never see any hard evidence that Apple is profiling users and that ios/mac are not significantly more private than android/windows. Only a lot of "Apple is equally bad, just trust me bro" posts.
I use Orion on iOS which actually does support both firefox and chrome extensions (though very much a work in progress compared to the mac OS version). Ublock origin doesn't work unfortunately but the built in content blocker is pretty much just as good. Orion is noticeably snappier to load pages than Safari (I guess because it doesn't have Apple's telemetry?), blocks all youtube ads, and can use Kagi as the default search engine. Just because every browser on iOS has to use the same rendering engine doesn't mean they don't come with their own features or perform the same in terms of speed.
OTOH with Safari you do get better extension support through the app store, can use iCloud private relay, and is theoretically better in terms of fingerprinting.