The US has alot of options in their top 6 for wingers. And some more polished two-way players for their bottom 6.
I don't think him saying Boeser is on the bubble is a slight to Brock, I think he's simply challenging him to standout among the other potential roster players. I wouldn't be surprised if Wilson has a dozen players he considers "on the bubble" with 9 players still to cut from the 32 camp invitees.