Compare as much as you want, but it will surprice me big time if
Yamaha (or anyone else) release a mid range model that match the
top of the range models for tousands of dollars less. If so, it
most be compared to the other brands they comete against, not
their own models.
Even if compare to the the "past generation" such as Tyros2, it
would be a kind of shoot it's own leg. Yamaha still want to gain
profit as well as keep a certain distance between the model range.
It's simply a matter of business.

Cheers
GJ