https://gmail.googleblog.com/2014/10/an-inbox-that-works-for...
Three things are highlighted:
Extraction of info from items and display (now in gmail)
Bundles (some made it into gmail)
Reminders, assists, and Snooze (now mostly in gmail)
So i'm not sure i'd agree with you here, but i definitely would agree that of the big three, bundling made it in the least :)
Where? “Categories” were in Gmail before Inbox, but there still doesn't seem to be any way to get them bundled in the inbox the way Inbox’s primary display does, though you can set them as separate inboxes.
Edit: and the gmail version of bundles has fewer categories than Inbox does
I have all "low priority" emails show up at 5pm when I'm winding down my workday to deal with them.
That's the kind of thing I'm going to miss the most.