Not necessarily. I know that this makes sense on the surface. You probably know that a turbocharger or a supercharger on an automobile makes a big difference in HP. Smaller changes in in a dirtbike make it perform in drastically different ways. The kdx 220 is made for trail riding. It has low end torque that the KX does not have. It gains some of this ability due to an undersized carb. The smaller carb increases intake velocity at slower speeds and helps the bike pull up steap tricky inclines. The KX is made for MX. It does not have near the low end response the kdx does however it will rev forever. The kx probably has the same size or larger carb as the kdx 220. Gearing and flywheel weights will change the personality as well.
Basically (engine) size does matter but it is not everything. If you want to jump and pull weelies, get the kx. If you want to trail ride the kdx 200 or 220 is the better choice.:cool: