Yeah, I came to ASUS from Netgear too. At least with the Orbi units I had, there was next to no configurability of the radio setup. ASUS is more configurable, but that also gives you more ways to shoot yourself in the foot.
The other thing I've learned since then is that turning the router's Tx power to max is frequently counterproductive. The limiting factor on wifi range is typically the client's Tx power, not the router's. Clients invariably have Tx power a lot less than a router's maximum, and usually you have no control over that. So if you turn your router all the way up, clients can "hear" it a lot further away than it can "hear" them, which leads to erratic performance and frustration. If you have a large place, or non-wifi-friendly interior walls, multiple APs usually work better than a single AP at max power. But for starters I'd move the Tx power slider to maybe 50% and see what happens.