I’ve found spark slow to launch and iffy when it comes to running in the background and keeping me notified promptly. It is not something I want to rely on when running through an airport.
You can delete the Apple Mail default app on iOS and really on MacOS too, but on Mac you have to disable SIP. If you google dosdude1 he also provides custom images of MacOS that expose more functionality than the default.
Regarding OP I have never had an issue with Gmail for iOS. Google’s iOS utilities in fact, I think work a lot better than Apple’s. But Apple has never really been a software company and they have drug their feet when it comes to platform independence.