That seems kind of insanely high.
I absolutely agree if your understanding of what Petry brings is that of your average HF poster.
On one of the most mediocre offensive teams in the League, with the worst powerplay in the League, Petry has managed to find himself 12th for points for defenseman. He is more than capable of playing 20+ minutes a night without being a liability at either end of the ice, and what he lacks in physical presence he makes up for in offensive capability and vision.
He is a guy that you can trust to be on the ice when Hedman isn't, or you can play him alongside Hedman and make that first pair offensively lethal. He is also signed at a sweet 5.5m for the next 3 years, which the Habs could also eat some of (in the deal I proposed, obviously the Habs eat a bit of cap to make it more enticing).
Petry is unequivocally a top 30D in the NHL for this season, and he likely would become your #1 guy on the right side playing with Hedman. Not only is he likely the best second pairing defenseman in the league after Parayko and maybe Ellis; he has proven that he can be a reliable #2 guy on the first pairing.
The draft pick is likely to be 29-31. Columbus's 2nd will be somewhere around the 50s, so the jump isn't as crazy as it seems.
Cal Foote is a great asset, but is a bit slow on the developmental side and I believe that having Weber as a mentor could do wonders for his future. He is in no way a bust or anything, but he is also not looking as great in the AHL as he did in the WHL.
Tyler Johnson is a fantastic player, signed to a pretty team friendly contract, but he is only a 50-60 point guy across his career, and he has played on some of the best offensive groups in the NHL. He would be a phenomenal 2C for Montreal and it would allow the Lightning to address an area of weakness (RD) while moving out a player from a position of extreme strength (C)