Interesting.I agree that Ablett tried his best last year, unfortunately his best is what killed us against Collingwood. He was all over the play in the first half, but most of the play seemed to linger in our defensive half - Collingwood's press was not focused on stopping Ablett, rather on killing Geelong's chain of possession 1 or 2 links after him - meaning that his trademark short handball to another player would get that player or the one after into a position where they would be forced to turn it over. This next theory is purely my own observation and perhaps reaching a little, but I believe Thompson identified this half back roundabout play as a weakness early, and that Ablett was a major factor in it continuing - hence moving him to the forward line for large stretches of games. Ablett of course was not happy with this, as he rightly considers himself Geelong's (or anyone's) number 1 banana - so after several weeks of increasing frustration and horn-locking with Thompson, the leadership group has approached Thompson and said that they want, for the sake of team unity, Ablett back in the midfield. Thompson agrees but immediately gets on the phone to Essendon with a "I'm done here, got a job? No not the senior one, senior coaching sucks and you get shitty with everyone". Ablett goes back into the midfield (and rarely goes forward at all for the remainder of the season) and the old "attack from half-back" style is resumed, also playing right into the hands of Malthouse's forward press/roman box tactic. Ablett was gone a long time ago anyway, Thompson was gone from late H/A season (but probably had thoughts of leaving from earlier since it was known that Costa was stepping down from the board. To me, the pieces all fit.
There's one bit though, that doesn't quite fit; or maybe fits on top of that.
In an article a couple of months back (possibly on Ablett? Or Thompson?) Bartel was saying the group chose not to go with Thompson's changes, much later on - heading towards finals; choosing instead to stick with tried & true.
IMHO, it's quite possible the Ablett & Costs things started to plant the seeds; Evans et al made sure they kept in touch and kept stoking the fire, and the final decision only came at that point leading into (or directly after) the prelim.