I agree theres definitely some positives, and for me, his story is one I cheer for, but theres been some concerns about his game from the beginning. I know I've been in on a few of those discussions so it's always been my version/opinion of history. I wrote a long post that was essentially a scouting repot, not going to do all that again because it was an incredibly poor use of time
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but highlights - Holl is a very good 1v1 defender. Whether on the rush or in the zone, he uses his stick and reach very effectively to play simple defense. Hes not a great skater but hes good on his edges which allows him to move well in close quarters, and he also makes a pretty good first pass as well as some creativity to use the boards or just hesitate or change the angle to make a play. All very good things.... but, where he struggles is when the simple play isn't right in front of him or he has to anticipate the next play. Nowhere is this more glaring than in d zone coverage where he often falls asleep, losing body position or just missing his check. He doesn't use his size and leverage to box out/tie up like he needs to, he'll often defend a wrap around the boards the far point from his corner then get beat back to the net and allow a player free to either screen or deflect a potential point shot etc etc. So many little details that often go overlooked if they don't end up in the net, but ones that are sure to drive a coach crazy.
While he never spoke on the subject to my knowledge, these critical flaws are my best guess as to why Babcock dismissed him so early despite some obvious positives.