If two 5.0 WLANs broadcasting from one AP is important to your application, then the AC5300 would be your "higher spec" router... but if stronger processing, hardware encryption, or ~20% better WiFi range is the priority; then the AC86U would be your higher spec router. If you want to enjoy longer/stronger firmware support including fixes, security patches, and AiMesh improvements; then the newer AC86U might arguably be the higher spec router. You decide for your needs... but compare apples to apples... if you need 20% better WiFi coverage from your AP, don't give it up for a hamstrung second WLAN crammed into the narrow/DFS-restricted 5.0 band that you may not need or which could unnecessarily complicate your radio network and its administration.
OE
This is the part about AiMesh that I seek to better understand. To carry on your analogy, I have apple, orange, and pear. In AiMesh, does each fruit bring the best of itself to the party? The 86 has a better CPU and possibly more patches when compared to 88 or 5300, which makes it an ideal root AP. In this scenario, will the 5300, as a participating node, still provide two 5Ghz networks?
Notwithstanding the reliability or effectiveness of SmartConnect, I plan to test it and see how well it works. Restating the above, with AiMesh and SC interoperating among 86 (as root), 88, and 5300, will it fully utilize each of the device's unique hardware advantages? That is, 86 being leveraged as the best mesh "processor" and offering 3x3, 88 offering 4x4, and 5300 offering two 5Ghz, etc.?
I would hope that AiMesh would operate as I imagined. It would be silly to only be able to use the 5300's two 5Ghz if it were the mesh root, or enjoy the 88's 4x4 if it were the root. With SC, one would hope that the client will be steered to the best 5Ghz network.
Your point about not adding more network than required is well heeded. These are more academic questions to better understand how AiMesh works among disparate hardware and how to best leverage each node's capabilities--assuming, for example, that the two 5Ghz can be a benefit to my setup as well as the faster CPU of the 86, 4x4 of the 88.
I'd appreciate your thoughts, OE.