The future is probably just having multiple wifi APs wired up and then just running extremely fast but low range wifi.
Also, your glass door probably has Low-E glass which has a metallic coating.
> The future is probably just having multiple wifi APs wired up and then just running extremely fast but low range wifi.
This is somewhat the case, but it is limited. For example, in 5GHz there are 21x 20MHz channels available. In a highly dense environment, this can support roughly 30x devices per channel well and 50x devices per channel with some degradation.
Limiting the TX power on an AP can help, but it's not a panacea since clients always transmit their control frames at their default power (usually ~15dBm). There have been some improvements to this in .11ax, but depending on the spatial organization of the devices, it can only do so much.
Well, what if you want wifi in your garden? Maybe you own a few acres of property and you want wifi for a wedding? Now you actually have to do a minor bit of planning. Supported wifi versions, max EIRP, range, modulation rate, throughput, XPIC, coverage area, frequency, beamwidth, MU-MIMO, does the frequency require prior coordination with any government entity, etc.
I'm just giving a different use-case on the other end of the spectrum, to be fair. I agree 100% with your analysis however, we're going to mmwave frequency ranges with small but many APs. Massive Multi User MIMO, etc.
My guess is people with large houses and only one wifi AP are probably using 2.4 when their devices are out of range for 5. But other people doing this probably doesn't impact you at all since you can just make sure you have good coverage for 5ghz and enjoy uncongested wifi.