Lou was a very important part of this rebuild. Not only was he at the helm for the acquisition of some of the guys that are very important now, he also brought much needed credibility and stability to the role and the organization.
Having said this, I believe Lou gets a free pass on his performance grades because of his legacy and reputation. I like Lou and he obviously has a history of results, but hasn't won a cup in almost 20 years and his last cup final was 8 years ago.
Since then he has made some questionable moves to be sure and these almost always result in his teams having cap trouble. He values the veterans and intangibles and maybe that can be a strategy that pays off, but it hasn't in a while for Lou and IMO his current Islanders are getting further from the Stanley Cup rather than closer.
He had a lot of money and term tied up in guys like Lee, Bailey, Pageau, and Palmeiri but had to bridge Barzal (that will become expensive) and give away Toews and possibly soon Mayfield. His goalies are $9M of mediocre. There are lot of questionable cap moves for sure. The prospect pipeline is not exactly stocked either.
He was brought in to give the Leafs stability and to mentor and bridge time until Dubas was ready, that's why I believe was always Shanny's plan. He did a good job, but he is not responsible for signing any of the core 4 and left Dubas somewhat handcuffed in signing 3 of them. Could they have been singed earlier? He also left us Marleau and Zaitsev. Those are two of the worst Leaf contracts of the past 20 years.