"Mobile doesn't scale in cities" is the exact reason they need 6Ghz (because higher frequencies enable much higher density of cells, reducing terminals per cell). 6Ghz will penetrate buildings terribly, I agree, but it's honestly just not that simple, for example it's now becoming really common for carriers to be doing in building deployments; shopping centres, sports stadiums, the transit network (e.g 4g in the subway) hospitals, the list goes on. Secondly by lifting terminals off of say 800Mhz or 1.8Ghz band and into 6Ghz outside where you can, you free up capacity on those lower frequency bands that do penetrate buildings or reach weird areas like the middle of a park that has tree cover (or whatever).
Wimax hasn't been something anybody I've known in the US has talked about for more than 15 years.
I've built fiber networks and fixed wireless networks. Almost ended up becoming an LTE network as well. It didn't make any sense in any sort of financial modeling, even with spectrum availability.
LTE helps solve "general connectivity". What it does not do is build scalable, reliable, high speed, economical sensitive broadband infrastructure.
It was around that same timeframe that "TV Whitespace" was going to become the next big thing.
Anyway, LTE should be the literal last option. It requires more than 2x as many towers as fixed wireless, with gear more than 20x more expensive. That's also more than 2x-3x the required amount of of battery backup systems, networking equipment, and land / tower leases.
If you have extreme density, you NEED fiber and you need WiFi. You extend from the fiber network with extremely high quality ngFW. To fill gaps, use satellite.
Fiber requires a certain density of subscriber/mile(km), the same as any technology.
Even with 0 labor cost, you still need to get conduit in the ground (materials), fiber, terminations, switching, routing, OLT/ONT cost, handholes, any permitting or utilities location, horizontal boring equipment , jackhammers, splicers, etc. The upfront cost is many, many, many times higher for fiber and if you're okay with your cost-per passing being more than you would ever make on customer ARPU, then sure do that. Even if labor cost was 0. And it will take YEARS longer to deploy and see a return on investment from, of ever.
It doesn't matter if there's broadband to the location if nobody at the location can afford it.
5-6Ghz, certainly, lower frequencies do though. This is why T-mobile offers home broadband using their 5G network (which can support up to 1M devices per square km) in the US; they overbuilt, and have many smaller cells with lots of capacity and are undersubscribed, and monetize the remaining capacity using lowest priority fixed broadband.
One could see India deploying the same density compatible infrastructure in the usual "leapfrog" model of skipping lesser technology implementations in this space.