While I don't think ratings like PC, GB, push/pull and velocity are irrelevant. I do think they are all secondary ratings that mean vey little when benchmarked against the more primary ratings.
PC
There are many types of C's. The big bat C that is not very good behind the plate at all, but gives you .850+ OPS. The well rounded C that still gives you 800 OPS and has just above league average defense. The Big PC C that can't hit and can't throw. The extreme defensive C with 80+ in arm, arm strength and PC, but can't hit. The DITR C that is well rounded, but lacks arm strength. What I've found is that many of the above work out fine. The only ones I stay away from are the ones that have a big PC (85+), but below rec in arm and arm strength and can't hit. If you're going to go with a Defensive C that can't hit, make sure he has it all on defense. It doesn't make much sense to have a. .600 OPS bat in the lineup unless he is both helping the pitcher and preventing base stealing.
Velocity
I think in extreme hitters parks, the velocity rating can help as long as the pitcher also has good control, splits and pitches. You don't want to target pitchers with 60 splits, 70 pitches and 95+ velocity, but the pitcher with 75 across the board primary ratings and a velocity rating of 90+ will likely make a difference compared to the same pitcher with a below 30 rating in velocity. Velocity gives the pitcher an uptick in K's. More K's, less balls in play that the stadium can turn into hits or homeruns.
GB
The groundball rating is likely the most significant secondary rating. However, it works much better in tandem with great infield defense. Having a high groundball rate and a below rec SS or 2B doesn't do you much good.
Push/pull
Likely the least significant secondary rating. I used it in Wichita when I was trying to be cute. I tried to load up my lineup with Leftie pull hitters or rightie push hitters to take advantage of the difference between the LF wall and RF wall. My issue with it is that it's a secondary rating. It should not be something that is solely focused on.