As a diehard Raptors fan I will chime in.
Dwane Casey is a completely average coach. Sucks in the playoffs. No adjustments. Had all regular season to experiment with lineups just in case we needed Plan B, C, D etc to stop CLE's lineups. He did nothing. Rolled Ibaka + Valanciunas for 82 games and then was like, "Oh shit we can't start both against CLE". Too late.
Newsflash: Cleveland is going to go small. They've done it 3 years in a row to us!
I actually love DeRozan. As does every Raptors fan. But he's not a great player. Raptors have been better with him off the court for like 5 years in a row. He's an abomination defensively. His biggest strength is he gives you slightly above average offence and can do it for tons of possessions. This skill set is better on a team who is trash and needs someone to shoulder the load.
But on a contending team you need better than garbage defence + slightly above average offence from your best player.
The Raptors are/were good because Lowry is much better than Derozan. And their bench players are all starting caliber players. The new coach Nick Nurse is way ahead of Casey in mindset. He's new school and actually uses mathematics to come to decisions. Casey is old school.