Probably you are right about Holt, or probably not. IDK. Honestly I would give him a chance, if I wanted an average OF, but that's me. Low risk/High reward. If he shits the bed, you could have payroll flexibility, thing that you could be losing with Castillo if he shits the bed.
On the other hand, if I wanted an average OF, I'd never ever give Castillo's contract to anyone. I would use another strategy.