Lets reinforce this point.
First understand how Wifi works:
1. Spectrum is contended. Only 1 device, client or AP can talk on a specific channel, and they do this by a mechanism called Carrier Sense Multiple Access with Collision Avoidance (CCMA/CA). Not only does a device have to wait for other devices in your home, but any neighbours that are using the same channel too (within specific dB noise parameters).
2. Mesh wifi will require a dedicated channel, preferably a wide channel to do 'backhaul'. This means a large chunk of the capacity of the AP is dedicated to backhaul, while the other half is dedicated to clients. So effectively total bandwidth is halved, though as you'll never see max Wifi PHY bandwidth, it's not really a big problem, and why Mesh systems 'work OK'.
3. Clients that have a weak signal will use significantly more airtime since bandwidth has to be reduced. Wifi performs at the speed of the worst client of the network.
For more info you can read quite a good guide here: https://arstechnica.com/gadgets/2020/01/how-ars-test...
Now with Ethernet backhaul:
- APs can run on independent clear channels, which means you can make use of even more spectrum for clients, and if you have 3 APs in 2.4GHz with 20MHz channels and about 5 in 5GHz with 80MHz channels you can get full spectrum coverage of the entire wifi spectrum.
- Because backhaul is handled by Ethernet, you're not lopping off a significant amount of radios in APs to handle backhaul. It's entirely devoted to clients.
- This can be tuned for capacity (100s to 1000s of clients) or performance (wider channels)
- There is no interference on Ethernet backhaul, and with a switched backhaul, you have clear point-to-point uninterfered-with gigabit+ pure bandwidth. Let the switches and routers handle traffic, and APs solely for bridging radio and Ethernet. Really the biggest problem you have with Ethernet backhaul is mitigating broadcast and multicast (another issue entirely).
As for Wifi 6 or Wifi 5, remember the point that Wifi will work at the speed of the slowest device. If you have a Wifi 6 (802.11ax) network, but one Wifi 3 (802.11g) device, then all those Wifi 6 devices have to operate at Wifi 3 speeds for that specific channel.
This is why we try to segregate spectrum and put old devices on 2.4GHz on a small 20MHz channel and then have all our shiny stuff on 80MHz channels in the 5GHz superhighway.
So if you want the best, invest in putting CAT6 or 7 to every room, and have an AP on the lowest power possible in each room covering different channels and giving a very hot coverage in the room, and very cold coverage outside the room. That way, client devices will roam from one AP to the other, and always choose to pick the strongest signal.
For the same reason a mesh system even though you're sacrificing half the bandwidth will still be better than a Big Box parked in the corner of a house serving everything, which is the worst option.
There are many other factors like DFS (Wifi kit has to give way to radar), and other quirks about RF that matter, but the basic points are as above. Ethernet will ALWAYS win as backhaul. Same reasons in the 5G vs FTTP argument: it's no contest.