So you'd trade any player for a better player? How profound. Nobody is arguing against that meaningless platitude. This whole conversation spawned from a discussion about trading our top prospects for one of Trouba, Fowler, or Shattenkirk. None of whom are top defensemen. That's where your scenario falls apart, as has been pointed out. But you keep beating this drum for some reason.
Despite all the gushing over these guys from the LGW faithful, all of Trouba, Fowler, and Shattenkirk have real holes in their games. Trouba, for instance, has been heralded as a "potential 1D" despite showing Danny Dekeyser like offensive skills during his pro career. None of these guys are top defensemen on their teams. The fact that they'd be a top defenseman on our team doesn't make them better players, it just means we're not that great. If your 1D is worse than all the other 1D around the league you're still at a relative loss. And that's BEFORE you factor in the fact that you lost a top prospect to make it happen.
I'd have been happy to trade for ANY of them if we'd landed a decent offensive player in FA. Replacing Nyquist or Tatar with Okposo would have made one of them expendable. And a trade would have made sense. But doing it now, with a top prospect, is a recipe for disaster.