Just looking at yearly totals to judge McGroarty (and Yager, for that matter) is just mind numbingly lazy. McGroarty struggled to adjust to the pro game to start the year, but has really hit his stride and is allegedly playing great according to the WBS coach. His production has also really ramped up since his rough start. Yager was on a bad team to start the year and is now on a better team, his production last year was inflated from being on a monster team so this sort of plateauing isn't unexpected. The same thing has happened this year with Tanner Howe, he's been on fire since going from Regina to Calgary.
Both guys are B+ prospects and I'd still take McGroarty over Yager, mostly based on how safe of a prospect McGroarty is. I think the two have similar upsides (both top-6 complementary players), but McGroarty seems like a guaranteed NHLer while Yager might not pan out. That's not saying Yager has a huge bust risk, I just think McGroarty's bust risk is lower.