The grip and the trigger pull on the P30 is a lot different than the other guns you compared them to shield w apex, sigs. I personally never liked the double action on them and all my P30s are light LEM. I much prefer the trigger pull on my vp9 (but I'm used to strikers) and for HKs prefer their single action match trigger (only available on the USP). Having owned many USPs in different calibres and sizes, even each USP type shoots a little differently.
In regards to the SK in general, depending on your hand size that grip doesn't work as well because of how short it is. I've had some larger sized-hand friends have trouble with both the P30sk and the VP9sk.