What if it hadn't been ionic, but was instead the browser itself that rendered the same website differently when in different OS? Oh wait...that's already the case...
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.
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.