Good point, there are quite a few "mini" models out there that are low-ish power and would work well for this sort of application, and would likely have the horsepower left over to do other things that someone might find useful.
I haven't been watching the Linux+wifi space all that much lately, but what you outline still does sound much better than the situation even a decade ago. I get that it's slow, and I totally sympathize with and share your frustration there. I'm running 11ac gear at home, but I'll be due for a new laptop before too long, and would like to start the 11ax upgrade process. Seeing that I might have to forego OpenWRT (or just wait an uncertain amount of extra time) isn't really fun.
i do think perhaps im being a little glum about the wifi situation, even though we havent seen new/better hardware supported on openwrt for near half a decade. not just a "new standards" lag. on the hopeful side, codesourcery & others are doing a much much better job helping to make official open source image building a stable replicable manageable process. yes, almost always on linux 4.14 and or gcc-4 or ehstever and this infuriates me a bit, feels like a waste. but there is also more mainlinelining going on, both with cpus and with wifi cards. in fact it's almost just too well supported, that the problem is, now, that there's still not available hardware that has the new chips. for whatever reason the draft spec hardware all seemed to have bad errata, low/no drivers. and we just havent seen modern platforms with both the newer cpus and the newer wifi. still just not much hardware in general, even though draft spec equipment has been around for i believe years. progress isnt totally like i want but definitely some good signs too, and some just regular old "it takes a long long time before most chips start making their way jnto products". kudos to the hardwork of many who have been mainlining your drivers. you are doong the right thing. the future is exciting.