I tend to "group" pitchers, and it seems that most here are saying the same thing. Obviously, a pitcher with 90 control, 85/85 splits, 3 70 plus rated pitches and high groundball/velocity, is going to be a CY young / Fireman award candidate, but assuming you're looking to see what kind of pitcher can be "salvaged", or at least made to work when you dont have an ace, this is generally my thought process.
First thing I look at is control - If you have low control (below 50), thats a red flag. Typically if their splits arent above 75, this is going to be a bad pitcher. The lower the control, the higher the splits need to be for me. Pitchers with low control and high splits tend to be either really good or really bad, and can vary from season to season, and definitely from game to game.
Next, I look at splits, vsR and then vsL. - usually, a vsR under 60 isnt going to be effective, though, Ive had a CY Young winner with 58. He did have a control in the 90s a strong y split, and he generally got lucky as hell that season. Mediocre splits with good control, tend to be reliably mediocre (instead of wildly up and down game to game/ season to season like low control, high split)
Next I look at pitch quality - This is something Im looking at more lately, Ive never really examined a pitcher with both mediocre control and splits, but had high pitch quality, though it seems to me, that 1-2 really good pitches tend to make the average pitcher good, good pitchers better, and better pitchers dominant.
For me this is a rough "rating benchmark"
below 50 - Poor
50-60 - mediocre
60-70 - average to solid
70-80 - good
80 and up - Great