Here's what I think.

The Evo IX is the final "evolution" of the Lancer Cedia CT9A chassis, so it'd make sense that it would be the "best" version of all the CT9A-based Evos (VII, VIII, IX). Mitsu's boffins have had since 2001 to work on the Cedia chassis so it would be natural for the Evo IX to become the best iteration of them all.

This opinion is similar to how "dull" and "heavy" the same fanboys found the Evo VII compared to the previous-generation-chassis Evo VI, which is by the same logic the "best" Evo based on the Lancer CP9A "pizza" chassis.

The Evo X is essentially a blank-sheet creation; heck even the 4B11T engine is all-new (no 4G63T here, old-schoolers). Mitsu boffins will have just about the same amount of time to refine this car...or "evolve" it if you will.