I've seen tale of the tape. Morales had bigger thighs. Mosley had bigger thighs. Mayweather had bigger thighs. Pacquiao doesnt have big legs. Hes a very small man.
I'm talking about legs which includes calf muscles....are they bigger than mine? No I'm 6ft and have cycled in the hills all my life and I'm built like a brick shithouse....does Pac have well developed legs for a boxer his size ? Yes. it isn't up for debate as it's been mentioned several times in his fights by the commentary team. I'm not sure why you have an issue processing a simple fact.
I think it helps staying upright too. Remember when Mosley caught Floyd with a big punch? He was on his way down but his legs saved him.