I haven't liked Lou's asset management very much. Leivo for instance is completely wasted, they sold Kessel for far too little and the Marleau signing was unnecessary and will handcuff them when it comes time to negotiate extensions. Zaitsev contract was too much too soon and is looking terrible at this point in time. The defense still hasn't been fixed. You can hardly credit him for winning the lottery either.
Kessel was traded before Lou.
The Marleau deal I'd argue hardly handcuffs them because of the way that it's structured. It's so badly front-loaded that Marleau is barely getting anything on the 3rd year of the deal, it really wouldn't surprise me if Marleau and the Leafs agree that he'll be moved(to retire) at the end of that year to a team trying to get to the cap floor. But essentially, they added a vet with size, strength, speed, two-way ability and 20+ goal scoring ability for nothing but cash.
The Leivo thing really isn't on Lou as it is on the coach. After all it was Lou that protected Leivo in the expansion draft and given him a contract extension.
Zaitsev definitely has room to improve, he's still a sophomore to the NHL. But to get a Dman for 4.5 that logs big minutes that can play both PK and PP is the going rate.
You can't rush to fix the defence. The Leafs haven't made any knee jerk trades to improve the defence. Look at the Leafs timetable, I don't think anyone expected them to be this good this fast, so it makes sense why the team has been patient with their D. They have high end prospects on D(Liljegren and Dermott) and have the assets to acquire another Dman if it makes sense.
He was also the GM the pulled off the Andersen trade, and where would the Leafs be without that. That is the single most important move in this rebuild so far(minus AM34 obviously). But having a stud goaltender that can allow the young guys to make mistakes and still provide solid goaltending was great for their growth.