It's not just the antennae that make up the RF chain that makes Asus routers superior (specifically RT and GT model lines). It is attention to all the parts in those links. Including the SoC, the radio modules/CPUs, any amplifiers used, and many other peripheral factors, such as optimized drivers, SDKs, and other factors that other manufacturers don't seem to consider (from experience).
While the RT-AC86Us were the pinnacle of AC-class WiFi routers, they have long been superseded by AX-class equipment for a long time now.
Note that a single, entry-level RT-AX68U (sadly, EOL today), is drastically superior to the old king (actually 2x RT-AC86U) in the link below.
There are some odd regressions being discussed on the dnsmasq-discuss list from the PiHole guy (Dominik). https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2021q3/015598.html https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2021q3/015596.html I see Merlin is testing 2.86 out...
www.snbforums.com
Doubling the throughput while having the same or better range is what makes the upgrade to an AX-class router today more than worthwhile, particularly if you have the ISP speeds to take advantage of them (the current bang for the buck model today is the RT-AX88U Pro). And having a cooler running and more responsive router/network too.