Allen has had struggles with inconsistency, cheating, over-extention and poor positioning his whole career. There were noticeable differences in his play the back half of the season compared to how he played prior to Corsi. Corsi may have almost ruined Allen as he was at his worse during that stretch, but there were serious holes in his game before Corsi got here that Brodeur/Conklin seemed to fix.
But you are right, we don't know the extent of things, and I am definitely reserving judgement.
Well, I think it's probably more complicated than x coach or y coach ruined or fixed Allen.
But as far as Alexander goes, he's the guy that Allen works with in the summers. For all of his flaws, Allen always seems to come into the season well-prepared and ready to take on the season. But when Corsi, or Conklin, or whoever, come in and change his routines at the start of the season, and change his drills, and he isn't getting the same kind of interaction he thrives under with Alexander (by his own estimation), he starts to falter a bit. If nothing else, this move will add some more consistency to Allen's year, which I think will do wonders for his performance. Alexander clearly communicates in a way that resonates with Allen, so it makes sense to have him on the staff.
The guy is a great goalie, and he's still growing into the big boy job, but I think that he's got what it takes. If Alexander is the guy that can keep his nose to the grindstone and help him up when he falls, then great. If not, then we've ruled that option out and we can move on from there (whatever that means).
I wouldn't be surprised to see Allen put up a season like he had in Chicago in 13-14 this year. Having Yeo (who is easier to play for than Hitch), and his system (which made a god of Devan Dubnyk) will go a long way to helping Jake out in that regard.
