It's certainly possible they're optimistic, but at the same time, Baez's near 3 win performance didn't really include any outliers, plus on another team he'd be even more valuable as a full-time SS. He obviously has room to grow offensively and has already made strides, so further improvement isn't out of the question either. As for Schwarber, he played at a 4-5 win pace in 2015 with less than a third of his PAs coming as a catcher, so there's some built in regression allowed there too. I'm comfortable calling him a LH Nelson Cruz, for example, maybe slightly less bat and a little more glove. If the White Sox think Baez's bat is a time bomb or that Schwarber is a -20 LF then that would change things, but like I alluded to before, we have to assume they like the players in question to consider trading for them, otherwise their exact surplus value doesn't matter. In any case, I was also optimistic both ways. Quintana fell short of 5 wins each of the last two years, Sale regressed a bit peripherally but we'll assume that was intentional, and neither are penalized for the much higher injury risk they carry as pitchers. For surplus value, it was a quick 8 x WAR per season minus their salary, which I back of the enveloped to be 25M for Baez and ~30M for Schwarber through arbitration. Arbitration salaries might look very different in 4+ years, but that gets into complexity that is beyond the point I was making, since I wasn't inflating the cost per win each successive year either.