@baud I'm sorry to hear about your issues with the 'AX86U's. None of my customers have had any issues, nor I with my 2 units either, in the last few months. I don't buy network equipment online, I buy from a brick and mortar store (when possible). It is possible that you were getting units from a bad batch?
Having had the RT-AC86U, RT-AX88U, and the RT-AX86U's, I can honestly say that each upgrade (in the order listed) was because of an enhanced experience when using the network for any task(s) at all.
The difference between the RT-AX86U and the RT-AX88U was very surprising actually because even with the older RT-AC86U, they all share the same basic hardware (CPU, etc.) 'specs'. Sure, more cores here or there, and more RAM, but they should be comparable when testing for a single client device on the same connection (yet there were obvious differences).
The upgrade from the 'AC86U to the 'AX88U the benefits could be put down to 'AX' being better, and to the two years between the two models where RF design, hardware tweaks, and other fine tunings could be 'reasonable', given the time frame.
The easily noticeable lower latency jump to the 'AX86U from the 'AX88U was not expected or as easily explainable though. (This
link here shows this isn't my imagination, either).
I tried every combination of an RT-AX58U, RT-AX88U, and RT-AX86U in wired AiMesh mode, and each time, the RT-AX86U was hindered significantly when another router was in the mix. I had no choice. I had to buy another RT-AX86U and see if the issue would be AiMesh itself, or, the other (lesser) routers.
I thought I was just 'testing' the RT-AX86U's when I had them in wired (
2.5GbE backhaul) AiMesh mode. Of course, I couldn't give them up after seeing what my 1Gbps symmetrical Fibre connection could actual do with them in the network. Particularly when I could achieve those speeds wirelessly too with at least my laptop and an Intel AX210 Wi-Fi 6E adaptor too.
386.1 Final 2x RT-AX86Us 2.5GbE Backhaul
When a properly setup wired AiMesh network with 2x RT-AX86U's is in place, there is nothing else in the consumer space that can compare (at least, with the routers I've had experience with).
Spending $20, $50, $100, and $150 or more on the now 'old' RT-AX88U is not a good buy today when the RT-AX86U is also a consideration/available.
I would be looking for a new source of RT-AX86U's to test with instead, or at least, make sure you double-check your testing of the unit you have now vs. the 'AX88U. If you're not seeing the same as I do, the set up may be the issue?
The above held true from RMerlin firmware 386.1 Beta 1 through to Beta 5, and to 386.1_0 release final.
Best Practice Update/Setup Router/AiMesh Node(s) 2021
Hope you find the 'AX88U at a reasonable price if it is still the best match for your network use.