That's a great example in that it's a no-brainer, but it's also a pretty terrible example in that it's beyond unreasonable considering there aren't many +'s to cover that gap between Barzal and Hintz.
I agree with the theory though, and I'd actually suggest that Gurianov would make the most sense in a package for an improvement. I'm not close to saying Hintz is a complete player, but I think he's probably closer to a complete player than Gurianov. Depending on the player coming back, Hintz obviously isn't untouchable, but I would definitely at least float Gurianov out there. He's due a big raise because of the 20+ goals, and while he's been a good piece for Dallas, you can't be sure he's more than a fast guy that scores off rush chances. That's a nice piece but it doesn't exactly make the guys around him better right now either.
It reminds me a little bit of what Nill did with Reilly Smith and Alex Chiasson when he took over the Dallas job. They weren't as far along in their development as Gurianov in terms of transitioning to the NHL so he has more value right now, but they were still considered very good young players. He flipped them in packages for more established players. I think the thing that is similar about Smith, Chiasson, and Gurianov is at the time they were traded or in Gurianov's case where he is right now, they looked like nice pieces you'd want on your team, but I don't think they're core, building block players either.