I'm not using ISP's router and instead bought my own Motorola SURFboard SB6121 about four years ago. It has served me well, but I think the issue is with the Apple AirPort Extreme Base Station that can't reach far enough. Every once in a while, I have dropouts and slow connection, and the solution is to restart (unplug, wait, and plug in again) Apple Airport Base Station.
Maybe a wireless mesh network is an overkill in my case, and getting a more robust and modern router will solve my range problem?
For example, this NETGEAR Nighthawk X6 supposedly covers up to 3500 sq ft. But at $220 it is close enough to the price of 3 Google Mesh points, each covering 1,500 square feet (4,500 sq ft of coverage for three).