Asus are the (insert your 'favorite' disgraced celebrity with a penchant for physical/sexual abuse here) of the networking world, everyone is aware that something is not right, there is clear documented evidence that they have done reprehensible things that no company anyone should want to support would do, they have been caught/fined so many times it's not even funny, leant nothing from it, and still they keep finding new ways to do the same old crap again and again.
For the op, you have wifi issues, nothing you have stated you want/need requires a new router, split wifi as a function with either a mesh system and *wired* backhaul if at all possible, or as a bare minimum dedicated radio backhaul, the other option is AP's which will give a functionally similar result at this point, mounting one in say the upstairs landing area (eg somewhere central and high) tends to give reasonable coverage in most properties, things like extensions where external walls become internal walls can change that. In terms of what to get, I am a big advocate for Deco, I bought about 6 pairs of them when they were cheap, i've put them into numerous friends and families properties when they actually have wifi issues, zero call backs after that. The only downsides are it's an app based set-up, you are limited to guest, IOT and normal networks, and you can't manage the channel usage, but it's actually pretty good from experience. Failing that I use Unifi for larger installs.
