just for comparison, IIRC when Cabrera was good, his RBI % was in the low 20's.
Logically, RBI% is mostly a corelate of batting average - all things being equal, if you have a high batting average you're going to have a high RBI%, but you still get some variation in RBI% between guys with similar BAs. And that makes some sense because it's clear watching play that some hitters good enough to have some control over their ABs, like Cabrera was, may be altering their approach with a man on 2nd. OTOH it's also logical to assume that some guys must do worse with the added pressure. It alwasys seemed pretty clear Miguel altered his approach to put the ball up the midde with RSIP, and that probably drove some marginal increase in his RBI% compared to a guy who didn't. I remember once attempting to normalize Prince Fielder vs Cabrera's RBI% vs their BA's and at least between those two there was a pretty good residual signal that Miguel's reliability with RISP was better than Prince's.
Also re BA. We know OPS is the much better measure of total batting value than BA - that's not an argument. But the case where you might care about BA vs OBP as the contribution to OPS is with that man on 2nd. A walk in that situation contributes as much to your OPS as single, but the single probably gets the guy home.