Iirc, it has been used for prostate cancer for years. Now that there are better T blocking drugs like Bica, Daro etc, its use has been discontinued/reduced. Long-term safety of every androgen including, Cypro, Bicalutamide, Flutamide, is questionable.
If you compare it to only T blocking effects of Bica(150), Cypro (50+mg), Fluta(700+mg), yes it is weak. How weak or strong it is, is debatable, and speaking very bluntly on it doesn't make any sense whatsoever.
Spironolactone has not been used for prostate cancer, however it's been wondered whether it can reduce the risk of prostate cancer.
Anyway, opinions are opinions...