I can honestly say he's a legitimate top 4 NHL D-man at 24 years old. Worth the money. His ceiling however is a #2 or #3. This could be a steal... and at worst you have a good top 4 guy at 4.5 million.
You can say he earned that role for 1 season, on a bottom-5 defensive unit in the league.
If you look at his comparable contracts they got fairly fleeced, the term is completely unwarranted. Josi, Lindholm, Klingberg, etc all received very similar deals**
**However, those players earned their contracts by playing several strong seasons in the NHL, several several seasons that were all better than Zaitsev's.
He's played 1 singular season in the league and while I realize they absorbed all difficult responsibilities to protect Gardiner's flaws, he was still over -20 in his only year in the league.
Even if it had 5mil cap hit but for only 4 years, it would be a better contract for the leafs.
I really just don't see the point in the astronomical term, that is only advisable when the player has long-term upside and can eventually make the contract a bargain. Zaitsev just doesn't have a ton of upside, probably a #3 defender in the league is his peak.
There are PLENTY of downsides too. His downside is a 3rd pairing / not even NHL defender / goes to KHL and isn't in the league.
He isn't an established career top-4 D who's been doing it for 10 years. He played the role once on a team that had no one else who could. KEY point.