What is missing from the A4/AR song mode and from the digis song mode is the offset parameter. It’s one of the most useful parameter of the song mode but for now, only OT has it. I use it all the time, creatively speaking it’s very powerful.
As a keyboard player I’d not have particularly cared about this…until I got the update to the Digitakt and found “Scales” a really nice add-on. Scales on the A4 would be super please.