It’s not just the Raptors/switch over. In fact, that’s actually a smart part of it.
When the ACC was being built, there was no hockey planned to be in it. It was meant to be a concert and basketball venue.
Halfway through, is when things were purchased and the plans changed to move the Leafs into there and close MLG.
Since there was no hockey originally planned, they had to alter the plans as much as they could given what had already been built. It left very little room for the ice cooling system room. Meaning the Leafs, actually don’t have as large of a set up for the cooling, as other teams in the league.
Now, they’ve upgraded the machines since then, and from what I know, the ice is better now than it even was back in the mid 2000’s.
TLDR: While covering the ice to put in the basketball court does affect the ice some, the actual issue is the Leafs ice cooling systems are smaller than other teams around the league.