IMHO, Apps can look (and maybe even "feel") any way they want. But when it comes to integration into the system, they should be as native as possible. It'S 2025 and I can't drag and drop from/to the Gmail app on iOS - that's ridiculous (especially because I can't have real-time push notifications for IMAP in the mail app for Gmail account, which as far as I know is also a limitation by the Gmail servers, not by IMAP itself).
I would like to see an UX research of what is actually important to match to the platform for the users.
The matching of the look is, from my experience, pretty low on the list. It's usually some interaction that doesn't exist or match that people complain about.
