pyometra

(New to all of this) My question is, is there like a rule of thumb for dog breeds that are less likely to get Pyometra as Ive read that overbreed breeds are weaker immune system?

I have some questions about females. Pyometra is fatal and it can be treatable with OSS and spaying, but I heard that it's not good to operate an OSS because with missing womb the vulva/pussy will maybe shrink and a male dog or a human could break the operation seal at end of the vulva/pussy...