> We need reliable, real-world ~20mbit/s for our warehouse scanners, not 382722 theoretical Gbit/s 5cm from the access point

Those two are the same thing, though!

Literally nobody is hitting those insane theoretical transmission speeds. Heck, most access points don't even have the uplink for it. So why bother? Easy: because it provides you margin. A 10Gbps link degrading to 100Mbps due to poor signal quality is a lot better than a 1Gbps link degrading to 10Mbps when you are trying to achieve that 20Mbps connection. The expectation is that your signal will degrade, so it is all about starting with a good-enough spec that you'll still have a reasonably-usable connection left at the end.

It's a similar story for multi-client connectivity. A 10Gbps link might sound overkill for a 500Mbps residential internet connection, until you've got legacy and poor-signal-quality clients taking of 95% of the airtime for 5Mbps of data. Being able to still get enough data through that remaining 5% airtime to saturate your internet connection is incredibly useful.

And before you praise DECT too much: its 2020 revision allows for a 1.2 Gbit/s transfer rate, with all the fancy stuff like MIMO and beamforming you might know from Wifi. Quite excessive for a few simple phone calls, wouldn't you think?