Seems like you know a bit about this. Could you indulge my curiosity and elaborate why wifi is shit? I assume some combo of DSP bottleneck (i.e. want to keep hw cheap) and maintaining backwards compatibility with older standards?
Multiple Access - this is the general term for 'multiple devices on the same spectrum'. Cellular divides up the spectrum into frequency bands (Frequency division multiplexing) and time slots in those bands (time division multiplexing). The base station then assigns each device a slot in a band (or potentially several), it also provides the time reference for this scheduling. This makes efficient use of your available spectrum and nothing interferes with or talks over anything else.
Wifi gets none of this. There's no base station planning so two access points can interfere with each other. There's no FDMA (access point runs on one channel of one band), and no TDMA. There's no uplink channel and downlink channel separation. Instead it's "Carrier sense with collision detection". Basically "try not to transmit at the same time as someone else, and if you do come back and try again later". This results in nodes competing, talking over each other, interfering (see "hidden node problem") etc. and makes inefficient use of the spectrum. The problem gets worse as the traffic gets busier. Wifi 6 is bringing in some actual scheduling.
Modulation schemes (the fundamental way that you transmit bits on a radio) - cellular modulation schemes are now incredibly efficient and robust. They use a variety of techniques that allow scaling based on channel conditions so that you can get as close as possible to whatever Shannon currently says you're allows. A lot of wifi uses old-school spread spectrum, and newer standards use OFDM which is a bit better. Wifi 6 is finally moving to the Quadrature Amplitude Modulation stuff that LTE uses.
That's why I find the smartsky comparison so interesting - because it's a completely level playing field.
I.e. the master channel is used to serve wifi to the nearby devices, and to the next wifi routers in a chain, whereas the slave channel is used to get wifi from any upstream routers.
We wouldn't describe that approach as FDMA - more that it has a separate channel for backhaul.
Cellular standards cater for a very different use case and, as a result, as vastly more complex and robust. To manage a lot of moving users and to support mobility is hard, also taking into account that cellular has had to deal with quality of service from the beginning because even if data rate was low voice requires a constant throughput with constrained delays.