From a personal experience, JS and JR aren't that much important for bigs (in LI offense). In fact, I don't consider them important at all. IS makes all the way the difference.
The problem is, as previously stated, the efficacy of ID, which is, as of now, not big enough. They need to make ID work better and match IS.
That means:
A big with 15 IS, should not have a bigger efficacy than 50%, if the Bigs on the other side have 15 ID.
Let's not mention SB, which is almost completely useless.