I, too, have been considering the AX86U to replace my AC88U, although the comments I've been reading here seem to be lukewarm about the AX86.
I thought I'd add a positive observation about a mesh system, in case it helps in any upgrade choices:
My main router is an AC88U running Merlin for 5 years with Comcast cable ISP, up to 250 Mbps. Then, about a year ago, I was given a 3-piece XD4 ZenWiFi AX1800 AiMesh.
In my limited experience, the XD4 AiMesh has been performing well for me connected to the AC88. With Ethernet backhaul on all nodes, I can get high-speed Wi-Fi connection anywhere in the house (2-stories, 2,400 sf). My Samsung S22 Ultra is a happy camper. I've used the XD4 both as (1) an AP (with self-contained 3-node AiMesh system) for the AC88 and (2) all three nodes connected to the AC88 AiMesh interface. (In the first case, all Wi-Fi clients connected to the XD4 show up as wired on the AC88.) Usually, the AC88 has a total of about 10 wired and 15 wireless clients.
Recently, I upgraded cable Internet speed to 1.2 Gbps. To verify ISP speed, I rented their gateway for a couple of weeks, and compared to a purchased Arris S33 which got the same speeds. Connected directly to the modem, the XD4 gave me > 900 Mbps to over 1 Gbps speed using Fast.com. (Yeah, chasing speed test numbers.) The built-in speed test in the AC88 only gets 400-500 Mbps (which I understand may be a red herring) connected directly to the modem. My computers are all old enough that I don't trust their speed capabilities for either LAN or Internet. But with a borrowed new laptop, I got > 900 Mbps Internet speed on all LAN ports of the AC88 (and on Wi-Fi in close proximity). I also get at least 350 Mbps Internet speed anywhere in the house with my phone (or at least 900 Mbps near any XD4 node if I reset Wi-Fi on the phone to connect to that node).
I considered just using the XD4 as the main router, but it's a bit skimpy on the UI features and doesn't do Merlin, so there's not as much to tinker with.