You might be right, Castillo struggles vs RHP. His split is nearly .300OPS difference
While in small sample, JBJ did a lot better vs LHP.
I think Castillo could learn and turn into a slightly above average player. He just has to stop with his gaf, misreading a flyball, fielding a ball hit at him, forgetting how many outs are there, and base running mistakes. Being an average hitter is just fine, but not with those peripherals. They're correctable.