The Habs did improve under Gainey, but that was largely due to positive momentum from the 1998 draft and the fact that Andre Savard was already turning the team around.
Gainey also had some good moves, like bringing in Kovalev, bringing in Hamrlik, trading Rivet for Gorges and a 1st, trading for Tanguay, and hiring Jacques Martin.
But he had significant failings.
He didn't negotiate contracts during the season. So the team ended up losing a lot of good players for nothing. Sourray, Streit, Koivu, Kovalev, Komisarek, etc.
He was too trusting. He expected other GMs to be nice and not take Beauchemin and Hainsey, silly.
He bought at the 2009 deadline when the 2008 deadline was more important.
He was obsessed with getting a center, but he failed. There were circuses around Sundin and Lecavalier. He then overpaid for Gomez. I understand getting Gomez, but he didn't need to overpay.