I agree but wouldnt there be a point of diminishing returns, in that we train chins for back and that even though the biceps are stronger in that position the range of motion is to much.
I dont know whether this is true or not, im going of personal experience, i could be wrong.
Chins = slightly wider than shoulder width and undergrip...
They are better because the biceps are put in their strongest position therefore you will be able to work the back with more weight/reps because they will be less of a weak link.