This is my thinking, 135 Loma is not a prime Loma............I believe he would win but he's going up against a behemoth LW in Castillo and we know that Castillo knows how to press the gas on elite boxer/punchers, he has wins over elite boxer punchers larger than Loma and Loma would have no choice but to concede ground because he won't be able to force Castillo to go backwards at any moment in that fight. This would be a very difficult style matchup for Loma when you really think about it.
Loma is not a typical boxer/puncher. He uses movement in an unorthodox way. I see it competitive for awhile but ultimately favor Loma perhaps via stoppage...NO MAS
Castillo too tough, too much grit and guile for a slickster like Loma. This is one of those fights where you'd walk away scratching your head thinking "did we spend too much time hyping this guy?"
I favour Loma but you have to remember Castillo beat a prime Mayweather so has performed at a higher level than Lomachenko ever has.
Casamayor was not the typical boxer/puncher and very unorthodox as well.................I personally see no possible way or scenario that Loma would ever cause Castillo to submit. The only way prime Castillo was stopped were by cuts and I don't think Loma has ever stopped anyone in that manner. I think Loma wins as well, but he'd have an extremely tough time getting the win.