@FBinNY The image in my head of endo-ing a seven foot long bicycle is both hilarious and terrifying. I played around with the cable angles and length, without seeing much improvement. I'd given both the rim and the pads a wipe down with alcohol, though I never though to roughen the pad surface. The pads weren't toed in at all; I set my brake pads parallel to the rim, and only toe them in if they squeak. Is this wrong?

@agmetal That's the hub I was mainly considering, or the XL-FDD with the dyno.

Anyway, there are probably multiple solutions here, but changing out the cantis for a V-brake worked, so I'm gonna call it good. Thanks to all for the advice!