When I pick a song and "Pro Drums" are available as an option, I assume you actually have a pro drum part (with differentiated cymbals and toms) for me to play. "Children of December" by the Slip has a long drum solo played on the toms, but the screen tells me to play the hi-hat and crash. Playing it is like trying to read a bunch of color words written in the wrong colors. (In Pro Mode if you hit the drum instead of the cymbal it counts as missing.) If you couldn't update all our old content for Pro Mode, fine, I have to live with that, but this is just wrong: a classic case of a half-assed feature being worse than no feature at all.
The idea that we might not ever get pro mode for old songs (even if we pay more) is sad, too.