Morales is a better boxer, but not enough better to overcome the size difference in this case. Castillo was also very very good. It's a bad match up for Morales, his long jab would not be as effective. Castillo UD.
their are some real **** ants on this site. erik morales has feasted on pressure fighters throughout his career, an extra 5 pound weight advantage for castillo wouldn't make much of a difference. it's an ATG vs a very good fighter. look at this older version of morales taking punches from maidana at 140. morales blows castillo off the atlas at any weight.
135 Morales would probably beat him, although Castillo had heart and made most fights tough. But Castillo is the kind of fighter Morales dominates stylistically.
Castillo was too big and too strong for Morales. Morales better career, but he does not beat the bigger Castillo.
At what weight? At 135 Morales was already way past his best. At that weight, I'd pick Castillo considering Castillo was in his prime there. Castillo is a little underrated because of how he ended his career. At lightweight, at his best, he was a damn fine fighter.
Castillo's size, body punching, and power would take a toll on Morales. He'd either win a clear decision or stop him late. Pound-for-pound, Morales is obviously the superior fighter though.