Derozan isn't really the engine of the team, it's Lowry. Heaving the most 2 point shots in the league will get you points, and it's useful in the regular season, but when your game is centered around mid range shooting and getting to the free throw line, your game tends to suffer when the whistles get put away in the playoffs.
Agree that adding Ibaka will give the other teams something to think about, but realistically this teams success is on Lowry, not Derozan.