Yeah 200MHz band guard is a massive guard. You can fit all of the FM band 4-5 times in that range. Also the resonate frequency water has a high attenuation factor so radio waves wouldn't be used there because they transferred a huge portion of there power to heat vibration water.
As for use cases it's a faster network in latency terms. There might be fewer use cases for it now but there were no use cases for WiFi before wifi exist. Once that infrastructure is built people will use it. By definition it's impossible to get a latency of less than 10ms on a large portion of LTE networks. If you have a sensor that requires a response that fast you simply won't use LTE because it's not possible to meet those mission requirements.
5G also has that beam forming whose goal is reduce congestion and solve the penetration issues but that is still being proven
As for use cases it's a faster network in latency terms. There might be fewer use cases for it now but there were no use cases for WiFi before wifi exist. Once that infrastructure is built people will use it. By definition it's impossible to get a latency of less than 10ms on a large portion of LTE networks. If you have a sensor that requires a response that fast you simply won't use LTE because it's not possible to meet those mission requirements.
5G also has that beam forming whose goal is reduce congestion and solve the penetration issues but that is still being proven