"new hot things" kinda screams "gaming" marketing for the kids. which the ax86u and ac86u are a part of. the only asus router i could recommend to people right now besides the ac66u_b1 and ac68u is the ax58u since the ax88u also seems to have similar problems and is ridiculously priced. And thats only if you have wifi 6 devices or absolutely need that extra range. The only thing "strong" about these new routers compared to the older models is the wireless range, and not by that much imo. Its more about high bandwidth and speed imo. They don't handle more devices any better and the firmware is so unstable its a downgrade in every other aspect. Most people running the ac86u can't even keep all the features enabled without the thing crashing. Thats a joke.
AImesh was a buggy unreliable mess for me to the point it became totally impractical. Even with a wired backhaul. I'm not buying that handful of beans anymore. Maybe if I had two ac86u's the aimesh node would of been more reliable? But as a standalone the ac86u was so buggy and unreliable in itself that it probably wouldn't matter. And the big selling point of aimesh is being able to use your old router like you are suggesting. But it doesn't always pan out in reality.
The avg home is going to have 50 iot and smart home devices soon in the future. They are going to want networks that don't crap out once a week so I don't know what the future holds for this consumer market, because at this point ISP routers are getting more reliable. The only reason to buy these routers as I did is to save on the monthly fees and for the extra functions, But if they are too unreliable people aren't going to bother.
I myself am going to move away from asus networking altogether. I personally tried the ax58u and ac86u and its just not worth it over the ac68u imo. It seems Asus is really milking the reputation they garnered from the legendary ac68u and are going downhill.
If you want (or need) a commercial/enterprise router for your home, you really shouldn't be looking at Asus: there are more appropriate solutions for you. I hope they're as magical and magnificent as you hope or believe they will be; I also hope you enjoy parting with your hard-earned money for the experience.
I'm running an ac86 for 2-ish years now, give or take, and havent had a single problem with it, other than with a couple of config blunders on my part. My experience differs from yours, obviously, because mine has been a rock solid piece of kit that I haven't hesitated to recommend to others because of that. Mind you, I'm just running a simple 2.4 and 5GHz wifi scheme, no guest networks, no VPN client/server, Native IPv6 on a 50/10 DSL, no dual wan, cake for qos, unbound DNS/blocking, no skynet, no suricata...no overreach.
I'll give you marketing: gamers trend towards the 5300s because they're explicitly marketed as Gaming routers to the gaming crowd, who then tend to come looking for advice on how to lower latency and find that their niche routers aren't as malleable as the mainstream ones. oh, the irony. right?
I also don't agree with you on the smart devices/IoT - 50 seems high to me: I'm doing whatever I can to limit my exposure to them.
Further, the ISP-provided modem/router combo box only does one of those acceptably well at any time for me (and many others), which is why companies like Asus make product in that category...and take them to a next step with tech like AiMesh. (I'm expecting v2 to bring home whatever runners are stranded out on base from v1 - a bit of patience might serve you well if youre so inclined - because alpha testers on both the factory and merlin forks are reporting improvements. by the time beta has wrapped and release is happening, it'll most likely be elegant/smooth or at least ridiculously functional for what it is)