Correct me if I'm wrong but aren't all high power rf finals tubes?
Also, from my ham experience, tube finals can take more of a beating than transistors.
Not in my industry - any more.
Until the early 2000's our RF amplifier output stage was a big, metal bottle vacuum tube. I am a Magnetic Resonance Imager (and CT Scanner) field engineer and the 20Kw amplifier - admitedly narrow band - worked in the 63Mhz frequency for 1.5Tesla. The latest models are solid sate, although due to 'black box technology' I am no longer required to know exactly how. Just change the FRU.
However, 3.0 Tesla magnets are becoming more popular for clinical use and those amps have gone back to thermionic valves - 35Kw at 127Mhz.
As for reliability, you may be right. I've only change a few 'tubes', but the solid state 'box' has failed far more.
Roger.