I totally agree with the lack of unified "All Sent" (and miss that after moving away from Apple Mail), and agree on Google being slow to adopt Files integration (though it was integrated by the time I moved to Gmail's app, so never had to live without this). But Gmail's app natively offering push, delay send, snooze, and accurately syncing across devices make it more competitive for my purposes at least. Ideally, this functionality could be more based on email functionality vs. platform specific API's, so it could work natively in Apple Mail, but I'm not sure if I see that happening anytime soon.