Not sure what "wouldn't do ruin" means.

However, as with medicine, you'd be getting into dangerous territory if you start to rate anyone by the highest success rate of cured cases. Just remember, for example, that the best (for whatever definition of "best") heart surgeons might be the ones given the most difficult and perhaps least-likely-to-survive cases. Their "success rate" when viewed naively might appear less than others'. At the other end of the spectrum, consider the neophyte homeopath who has only ever treated 10 cases of the common cold, each of which got better. Is this a 100% success rate ?