Not true at all. The AP can reply to 2.4GHz requests with a delay so that the device gets connected to the 5GHz network first. If the AP is really sure, it can also send a force disconnect. That's how most roaming is implemented these days.

We have a version of hostapd that will do this for you: https://gfiber.googlesource.com/vendor/opensource/hostap/

We call it "bandsteering".

> An AP cannot prioritize 5 GHz over 2 GHz. It's up to the client to decide what to connect to.

While this is strictly true, an AP can encourage clients to prefer 5Ghz over 2.4Ghz. How do I know? The enterprise APs from the big players do this and do it well. Recent versions of the software that drives UBNT's UniFi APs also do a good job of this. (Every client I've connected to my UniFi APs at home has always been steered to the 5Ghz band. [0])

Like IPv6 support (which the OnHub reportedly still lacks!), sometimes it's best to try and accept the occasional suboptimal result. :)

[0] And yes, without band steering these clients would always connect at 2.4Ghz because of its stronger signal. So, I know that band steering is working. :)

True, in my case I just wanted to turn off 2.4Ghz entirely but the software wouldn't let me.

My iPhone can't prioritize 5Ghz unfortunately. There was some BSSID trickery I could do, but having guests over was a pain since the broadcasted SSID would always result in a horrible connection. By turning off 2.4Ghz entirely on my old router there's no such problem (though the range is reduced quite a bit).