External routers: Do they matter much?

Hi!

I setup my Orbi (router + sat) in AP-mode connected to my old network (running on Asus RT-AC68U, dual band) with WiFi turned off.

My question is, how much is really needed from my router? Does a new tri-band (Asus RT-AC5300, for example) give me any benefit at all?

What's controlled via the router? DHCP and routing in general... will I benefit from tri-band/stronger CPU?

Any routers in particular that work exceptionally well with Orbi? I, like many others, live with the FREQUENT disconnects (sat disconnects from router, and mostly the router disconnects from my main router aswell, resulting in no internet at all).

Thanks in advance!