@anav, I think you discount he’s start at “hard” on the difficulty here. OP is lists:
Complete removal of AT&T router (“residential gateway”) from the picture
As someone who has AT&T Fiber service at my house. I do not do this myself, not because it’s a bad idea, but because “it’s too difficult”. So I post this using the Wi-Fi the AT&T gateway offers, which work fine for my needs. Thus totally get “don’t make me do CAPsMAN” attitude. We all have our limits of complexity we want to add.
But here… If you don’t use CAPsMAN, you don’t get roaming. It’s just that simple. And without roaming with multiple AP, users will notice. So like it, or not: it’s what Mikrotik offers. And to setup multiple APs on Mikrotik, CAPsMAN is the “right way” to do it. No one said easy.