Hello individualistic, libertarian caricature—
Catcher rating: I'm a believer in the power of catcher PC ratings, but I think it makes the most difference with pitchers who are on the edge of being pretty good or just slightly above average. I've had several examples of pitchers in the last few seasons who were regular 20-game winners with ERAs about 3, then I trade them to teams with mediocre catchers and they promptly fell apart. Exceptional pitchers will always be exceptional, and lousy ones will always be lousy.
CTL, splits and pitches are most important, and there's lots of debate as to how to rank those 3 in order of importance. My advice would be not to sweat 1 over another; just look for guys that are consistently good across all categories. That is, I think a guy who's control-splits-1st pitch are 85-65-65-85 won't be as good as a guy who is 75-75-75-75. Others might disagree.
About splits, do this simple exercise: find a couple righty and lefty SPs, then look at their split stats vRHB and LHB. The point there isn't to look at their effectiveness, but just the # of batters they face in each category. Check out the proportions of batters faced, and it will quickly become obvious how to assign relative values to each half of the splits.
And groundball ratio is a fun modifier that can make a huge difference, but for the vast majority of pitchers does nothing at all. Any rating between 30 and 70 makes very little difference on how frequently batters will ground or fly. Then take a look at guys with 80 ratings... and 90+. Find the guys with 90+ ratings for GB, and this rating becomes a true game changer. Take even a mediocre pitcher and double his chances for DPs and halve his chances to give up extra base hits, and he just became above average.
I've wanted to try the experiment of assembling a staff of all extreme GB pitchers (90+), then putting together the best defensive infield possible, and then abandoning defense in the outfield- just putting sluggers out there at all 3 spots, with no regard for range or anything. If all the pitchers bias the system toward ground balls 3:1 or so, then those outfielders should see only half as many balls hit there way, and the price for their defensive turdiness got trimmed. Maybe not as crazy as it sounds-