What would be "better equipment" in this case? Professional/enterprise/labatory radio equipment, rather than cell phones? CNC milled/3d printed racks rather than a cardboard box? I don't think there's much you can improve here.

They would fight hard to keep that data proprietary, as certain property owners might be more aggressive about lease pricing or royalties.

Many many years ago the FM radio station at college wanted to get FCC approval to increase broadcast power to 10 KW. In order to justify that, some students drove around taking signal strength measurements all over the area. They then picked the worst measurements to submit to the FCC.

This wasn't a violation of any rules. Let's say (for example) that the FCC submission needs 50 measurements spaced apart a certain distance. If you have actually taken 150 measurements then you can easily select a coherent set of 50 that show just how bad things are and justify why you need that 10 KW non-commercial license.

It's possible for the cell carriers to do something like this, but in reverse. It may make business sense for them to only retain/report measurement data that makes them look good?

Cell towers aren't cheap to put up. If carriers can obtain "decent" coverage with fewer towers, then it's smart for them to do that?

Of course, the carriers already have very very very granular data. They should be able to gather, and perhaps actually do gather, data from every single cellphone transmission as it establishes both voice and data connections. The carriers could/should use that information to erect more towers and to tweak antenna orientations on existing towers.

In my experience, however, this doesn't seem to happen. The same areas around me have dead spots that persist for years. This is in relatively flat suburban terrain, without too many large hills or tall buildings to interfere.

So in my anecdotal experience, Verizon doesn't give a shit about poor signal strength. And they're perhaps? the best at caring, so what does that say about the others?