135 is lightweight and Floyd knocked out Ricky Hatton at 147 which is welterweight. He also hurt a lot of guys at 147.
Woman take punches a lot worse than men, because of their whole body has less muscles(Boxers train their neck muscles like hell to get more punch resistance), less testosteron and so on.
Now add mma gloves, Ronda's non existent defense, her not rolling with punches and Floyd drops Ronda with everything but a Jab, hell maybe even with a Jab.
Darchinyan fights at 126 and started around 115 and he goes light on Ronda in sparring, tooling with her.