This topic has been addressed on multiple occasions [1, 2, 3].
To summarize: All iOS browsers currently employ Apple’s WebKit engine, which is actually open source. Utilizing any browser other than Safari introduces an additional entity to be trusted within the system. The advantages of using an alternative browser to Safari on iOS are minimal, if not potentially detrimental [4]. This is particularly true when Safari is fortified and used in conjunction with a content blocker like AdGuard [5].
Given that there are no alternative browser engines available for iOS other than Apple’s WebKit, it is largely impractical to replace Safari at the moment.