Schwarber has spent about 40% of his career PAs batting 1st or 2nd. Of his career 2579 PA's, only 1046 have been with men on base, 435 of which have been with just a man on 1B. That leaves only 611 with RISP. He has 35 carreer RBI and 153 career home runs. meaning he has driven in other runners 197 times. (Most sluggers drive in themselves more than anyone else.)
Schwarber has come up with 1,476 runners on base in his career and driven in 197 of them. Or roughly 13.3%. Most "RBI men" drive in about 14-18% of the runners on base. So he is just shy of this level of production, and a big part is he does tend to take A LOT of walks that rarely drive in runners.
JD Martinez has been better in this regard, driving in 17.9% of all runners on base (571 out of 3,176)...