non-chromium browsers only matter if the owner in question actually has any incentive to give users more control. Apple exercises even tighter control over their software than Google.
Firefox matters not because it's "not chromium" but because it's firefox, a non-profit dedicated to an open web.
Firefox matters because they're dedicated to an open web, but Firefox is usable by the general public because web developers are forced to support multiple engines if they want to work on iOS. These are two different things and both are important.
(Note: I've been running Gecko based browsers almost since the beginning. I guess in those days it was probably easier to use a browser that isn't perfectly supported, but I'd probably do it again if it came to it. But I can recommend Firefox to whoever I want, since it works on every site except Linked In. I couldn't do that if it only worked well on one in two or three or four sites.)
Firefox matters not because it's "not chromium" but because it's firefox, a non-profit dedicated to an open web.