Frost isn't competing with Brassard or Thompson. If he's as good as he's supposed to be, with two years to get stronger and understand his defensive responsibilities, then he should easily win the 3C job in camp. If he isn't that good, Laughton will be the 3C.
Laczynski, if healthy, will play ahead of Thompson, but he won't be parked in the press box if he can't beat out NAK for the 12th forward slot. That's a waste of time for a prospect, rather have him play big minutes at LHV and be available for the inevitable injury call up.
It's not a matter of expecting young players to fail, it's a matter of not giving them jobs, we've seen a number of players go to LHV and tear up the AHL and play well when they were recalled (Sanheim, Myers, Farabee, Allison), we've seen a number of players with meh AHL seasons and then fall short in the NHL (Kase, Bunnaman, Twarynski). Playing well in the AHL is not a guarantee of NHL success, but it's certainly a good indicator that a player may be ready for promotion.
Realistically, what are the odds that the 18 guys on the opening day roster make it through a season without injuries. In that case, every young player should be ready to "Wally Pipp" a starter. That's how most of the top teams deal with promoting prospects.