Personally, I don't think it is a protection anyway. Instead of riding with an appropriate gear, you have riders in top-level junior TT's wobbling violently constantly trying to push a gear that is massively too small. Much more likely to cause issues. Junior gearing is just a massively more stupid version of the kids lifting weights stunts growth myth, especially as even inexperienced riders with limited time on the bike will self select the most efficient cadence during extended maximal efforts and the gear that produces that.There are children out there playing far more dangerous sports than having too big a gear in fairness.