Tech9
Part of the Furniture
but now you are talking about ancient APs not ancient clients
We are talking about rare cases anyway. It can be old clients connected to old AP, but also old clients connected to modern AP with backwards compatibility. This AP understands the old clients and talks to them. Your router may not if some of the back compatibility was disabled by you.
We are also talking about as cheap as possible hardware home AIO router with bunch of settings found not working or doing nothing. N-only still listens for G. It allows N-only to connect, but not in greenfield mode. Disable B was found may not really disable B beacons (@sfx2000 on RT-AC68U tests I remember). Disable B was sticking in one firmware version with no reverse option except reset. Some IoTs were found have issues with disable B setting. Look at the first post - even Help pop-up in Asuswrt has bugs in it. The less you mess with this hardware the better. If someone is really after high performance this $50 home AP with somewhat working firmware and mostly BS marketing involved is not the right choice.