Thank you for answering everything I ever wondered about SiC. Are there any other semiconductors that would be even better than SiC in all four points?
Gallium Nitride is the closest competitor to SiC now; it's better than SiC for high frequency applications but worse for high temperature applications and GaN is somewhat harder to manufacture. But that's changing rapidly.
https://www.arrow.com/en/research-and-events/articles/silico...
It is also difficult to dope diamond n-type, as most of the donors are not shallow.
Interestingly: The conduction band in bulk diamond is above the vacuum level, meaning that conduction electrons "want" to fall out of the material. (Surface physics gets in the way.)