I think it's pretty common for prospects to be overrated for one's own favorite team, and underrate another team's prospect.
Stewart seems to me like a better prospect, but I might be overrating him and underrating Jenkins. My thought with Wheeler was that he was pitching in the same league as Jenkins this year and was about the same age, with kinda sorta similar stats. On a closer look, I would side with the other comp of Cederoth or another guy, like, maybe Mason Melotakis (before his recent TJ surgery news).
In any case, I think the Twins weren't really in the Heyward Sweepstakes, and that's ok. It would be great if the Twins can find an OF that can make up for the last two years of bad defense and mediocre hitting. They weren't likely to give up Kohl Stewart (or Melotakis, or Cederoth, or Berrios for sure) to get Heyward for a year, and there's no certainty that they'd be able to retain Heyward beyond that.
Dodgers, Red Sox, Saint Louis, all seem to have a surplus of bodies that could be MLB outfielders in 2015. Maybe there's a match there for the Twins...