Even one single salvo of the SAmurai Archers can kill +15 of the Monks, i've seen +20 lots of times. (120 men per unit) Even few Monks survive, they will be highly demoralized.

So even after your YS, never sent your Monks under an arrow fire, train Naginatas instead. (As Sasaki Kojiro said, running with your Daimyo to absorb the arrow fire is a bit of cheating.)

But i dont think defenders have any other bonuses, we feel that way because our crossing men feel alone and wavers much more quickly.