Interesting how others view your team. Like your ultimate conclusion, though I think that defensive inexperience let's someone get ahead of them
I actually think the review is more off base. Underwhelming isn't the correct word. Might pick frustrating. All 3 reasons you gave to say they were underwhelming were reasons there was tempered expectations last year. Hawkey was a backup to Ellis after missing most of his last junior season due to a severe knee injury, and as a backup played less than the average backup. Walman too was only back due to serious injury ending the previous season and it was clear in the time period you describe he was at least getting confident the next move was not going to reinsure himself. The Forward you refer to saw 6 newcomers in the top 12 3 in top 6. Frustrating was especially with veteran defense they didn't steal an early season game or that the offense disappeared late at playoff time. Also keep in mind team ended up in NCAA's, ranked, and just 2 points out of first and looking at your 2016 prediction you pegged them for 5th and as the 5th Hockey East team in the NCAA which suggests they were seeded just as you expected.
The issue with defensive inexperience is somewhat mitigated. For whatever reason Florentino was the 7th defenseman. Though replacing his and Walman goas is an offensive issue. A point you missed is that PC added Tommy Davis as a 5th year graduate student. So he lessens the inexperience
I also think you have profiled Mirageas incorrectly. Like Walman he's a 3rd round draft pick and a true freshman. McKenzie as a 20 year old in drafted players was strictly a shutdown defenseman not expected to grow his game considerably once at PC. You gave Mirageas' regular season numbers which were largely at Bloomington where due their team makeup wanted him to be more defensive. The Steel turned him loose offensively. You overlook then he was tops in assists in playoffs. I would think he stands an excellent chance of producing Walman freshman numbers.
I also suspect Conger will play a larger role than O'Neil. I believe Conger is competing for a 2nd line spot. O'Neil has to fight off Lemos and Hennessy for a 3rd/4th center slot