Not a bad trade proposal.
My opinion is extremely unpopular, especially on this site. But my opinion is that young prospects - even recently drafted first round picks - are not very valuable. My other opinion is that draft picks - even first round draft picks - are not very valuable. The two exceptions are: prospects who have done incredible things in their respective leagues; and first round draft picks inside the top 5 (maybe top 10) range. Those two things are extremely valuable, because they have a really good chance of, one day, becoming an impact player, possibly close to what a JT Miller or Timo Mier can do for example.
From Vancouver's perspective though, they are not good enough to even make the playoffs, never mind compete for the cup. Which means they don't really have use for a 100 point, all-situation 2-way centre like Miller. So that means they might have to trade him, no matter what return they can get. If that return is three lottery tickets, with 1/300 chance of winning, then it might be what they have to take. But it also means, they should probably trade every single player on their team, and start anew. Not a good situation.
I think for Pittsburgh that's a move that could put them in a really good position to win, and in my view, they are extremely unlikely to lose an impact player, and they are getting an immediate, guaranteed star, in either Meier or Miller. Also, Pittsburgh's 1sts will be late no matter what, but you add a superstar, and the 1sts are probably around 30th, instead of 20-30, which makes it even less of a loss for them. But again, I know on this site that prospects are infinitely more valuable than established superstars, and 1st round picks are even more valuable than prospects. So carry on.