Columbus wants defense, they know we're going forward and Philly likely is as well. They have no incentive to give up William Karlsson.
Also, I'm not moving below Philly for a 2nd round pick. The odds of hitting on a 2nd round pick are only about 30% and I would hate to see them take a guy like Barzal or Marner who kills us for 15 years.
The idea is this.
McDavid, Eichel, Strome, Marner, and Hanifin go in the top five. Order doesn't really matter. The next tier is Provorov, Barzal, Rantanen, Zacha, and Crouse.
Let's say the Devils don't have a particular favorite forward. They like Barzal, Rantanen, Zacha, and Crouse. They might have a favorite, but they don't think one particular guy is head over heels better than the rest. It's almost a sure guarantee that Columbus wants a D, same thing goes for San Jose. If you trade back with San Jose, that likely means that two D are gone. San Jose takes Provorov and Columbus takes Werenski or whoever they like. That would mean you still would have Barzal, Rantanen, Zacha, and Crouse to choose from -- depending on who Philly picks. Even if Columbus picks a forward, you still have two of Barzal, Rantanen, Crouse, and Zacha. It's very likely we could pick a player at 9 that we would have originally tried to get at 6.
Not only that, but we would pick up a third high second round pick. For a team devoid on forward prospects and assets, we now have three very valuable second round picks. If we use them all, we are going to have some very good forward prospects. If we trade them, we could get a good young NHL player. I just don't see what there is to lose.