Personally I really like the JS/JR on my C and PF as well. I have one Pf/C with proficient/average JS/JR who shot 8 out of 16 3p in 511 mins (50%) and another with strong/mediocre who shot 8 out of 25 (32%).
Compared with my 2 other PF/C that have bad JS/JR I'd say they try to shoot some more indeed (2 out of 5 and 1 out of 2). Of course there is a bit of bias since the other guys played C more often than PF.
But still I believe that my two big men with good JS/JR are fairly good at deciding when they'll get an easy 3pointer and the occasional easy 3pointshot helps my team. And proficient JS is not even that high considering my division so I think your guy will do even better.
Crunchy! If you eat fast enough