To add to that, the P Bruins are not owned by Boston Bruins, and their owner has a business to run, which means winning if they can and bringing in players to help do that. It has always been a weird situation since the GM (Evan Gold) is a Boston Bruins employee. I am curious how that all works, to be honest.
I do think that If Boston owned P-Bruins, you might see a different look with the franchise, but your bigger point is right in that there aren't enough good prospects in the Boston system to make signing the vets unnecessary. You will always need a few of them for leadership and culture, and mentoring (like Patrick Brown), though.