Maybe instead of an upper-baby mode you should just get better at the game
I agree. In GH3, I moved up very steadily from easy to expert. It was my first GH game, but I was used to the gameplay because I was AWESOME at Amplitude, one of Harmonix's previous titles. Maybe that made it easier for me to grasp everything, but like I said, it was a steady progression, and I was playing decently on hard in a few weeks. As it stands now, I can complete any song on hard, and maybe half the songs on expert.
As for Rock Band, I found Hard mode in guitar to be much easier than GH. The whole time I played, I failed one song, and that was in the final tier. Compare that to GH, where it took me dozens of tries to complete Knights of Cydonia or Raining Blood on Hard, and it's easy to tell which game has the more robust note charts.
And for the record, I find it much easier to stretch my pinky, so I play in the first position on the guitar. I know it sounds weird, but all of my pinkys are extremely... stretchy? Like, they can stretch really far away from the rest of my fingers. I include my toes in that, too. My pinky toes can move independently about an inch away from the fourth toe. Isn't that interesting?