Transferring spectrum from old to new users have proven to be much speedier and easier than imagined by PCAST and similar plans of 10 – 15 years ago. Getting governments and government agencies to cooperate is the harder problem.
The proper role of FAA in this and any similar controversy is to conduct its own measurements and share them with the responsible parties. It should share its findings on altimeter vulnerabilities and leave the modeling in 5G emissions to the experts.
Barring the advent of some new technology that allows you and your neighbors to use the same band at the same time with absolutely no interference, this is all there is. We will have have such a technology someday, but we quite have it yet.