It is just an opinion, but being able to just configure Discourse to use an address is still easier than creating a new inbox and password for each group and category you want Discourse to handle.
I’m pretty sure that this is the way that incoming mail is handled by CDCK and communiteq (and most sites I set up or maintain). So it is “standard” for Discourse.
I’d lke that too. I’m pretty sure that it’s no longer possible to set up a new mailbox for gmail either. I don’t know if CDCK has stopped using IMAP/Gmail and just using a mail receiver or what. I haven’t noticed any traffic on that topic lately (and am too lazy to search for it now).