It's hard for me to say for sure what has caused the rot problems I've had. My primary suspicion is that some of them became infected with
Fusarium or other diseases during their two-year stay in the boarding area of a commercial greenhouse, where they were kept very wet and, in winter, very cool. One of them definitely was, because I sent a sample to the plant pathology lab, and
Fusarium was detected in its tissues. So it may be misleading for me to say that rex is a pain in the arse, because I'm referring specifically to my plants, which have had some unusual living conditions.
Maybe as long as they are given standard Cattleya care with particular attention to getting lots of extra air to their roots, they may not be so difficult. My mounted rexes have done spectacularly. The potted ones have to be watched very carefully for signs of rot along the rhizome, checked daily. Aside from plenty of air at the roots, I'd suggest keeping their temperature range of 28°/18°C all year round, with as little variation as possible.
Then again, last year some put up
this post of their rex on Orchidboard and claimed to not give it any special treatment, and it looked fantastic, with more flowers than I've ever gotten. So that makes me feel that I am still clueless about these plants.