A few weeks ago, I was all, "Says who? Says physics!"
Well, according to Selected Canadian Spinning Wheels in Perspective, what I said was incomplete. It's not just the potential energy stored in a drive wheel that lets a large wheel do more work than a small one. It's (and here I turn to the book to get the terms correct) the differential in diameter between the drive wheel and the driven spindle or bobbin.
Larger drive wheel diameter means higher speed ratio. The speed ratio is figured out with an equation that reads speed of drive wheel over speed of bobbin equals diameter of drive wheel over diameter of bobbin (p. 65).
Speed ratio translates as mechanical advantage. The pulley system between the drive wheel and the bobbin acts to leverage the differential. The drive wheel's large circumference makes the drive band move quickly and because the bobbin turns with the drive band, all the benefit gets transferred.
So, nyaah on me.
I'm going back to my nice drop spindles now. They don't use pulley systems at all.