Google's browsers don't automatically load your websites with Google's visual branding and Apple's browsers don't load your websites with Apple's visual branding.
There's a battle between some of the large tech companies for appification of the Web at the moment, and that way of thinking is a trap.
You do realize that Ionic is mainly used for App Store and Google Play right? You're free to not use it. It's a correct decision for Ionic to go with iOS and Android standards, from my point of view, and the implementation is superb as always with Ionic components.
A company shouldn't design its website with Google or Apple's visual branding as if it were locked into a closed platform. It also appears to be a problem with things like Flutter, though I haven't looked closely.
There's a battle between some of the large tech companies for appification of the Web at the moment, and that way of thinking is a trap.