andriys the access list rule should not cause any problems, the delay is tiny, and most clients will not notice.
In fact they do cause major problems with some clients. I did an extensive testing before deploying a small CAPsMAN based network here. Most (if not all) Android clients I tested behave badly when using forced kick-off- a tiny barely noticeable delay when Android client roams itself becomes a huuuuge couple of seconds connection drop after each forced kick-off.
Modern Android versions (5.0+) are quite good at figuring out when to switch APs themselves, btw. Maybe with older versions this is a problem, but 5.0+ even does switch to 5 GHz aggressively. I have some OS X clients and their roaming behavior is much more conservative.
I don't think fiddling around with access lists is worth the hassle. Maybe MikroTik could add some kind of band steering, but unless this happens I'm already quite satisfied with the behavior of modern wireless clients.