The thing I'm not sure many NHL fans consider is that 18/19 year olds aren't exclusively thinking about the theoretical best way to stress test themselves for the sake of development. And in hockey unlike baseball, the players have agency over their progression.
Consider what Smith said on Saturday after the game:
Does that sound like a guy who is itching to leave campus after a few months and ditch guys like Gabe Perrault who he is roommates/best friends with so that he can go to the AHL for the sake of playing with other people?
To be clear, I don't think remaining in the NCAA, at least at certain programs, is mutually exclusive with player development. Cutter Gauthier went back for another year and he's a markedly better prospect now than he was at this time last year. Smith is only just now becoming more physical in games, and I think he could make huge strides there with another year in the system.
The quality of play and pool of players in the NCAA have both dramatically improved within the past few years in tandem with US youth hockey development as a whole breaking out. I think remaining in college for another year is going to become increasingly more popular rather than sending guys to lifeless AHL teams.