I only play franchise, I pitch on legend difficulty and it's so easy. The reason it's easy is because the cpu almost always takes the first few pitches. You can throw fastballs right down the middle and they don't swing. I have to turn up their hitting sliders so when they do make contact it's a threat.
Their ai needs to be tuned to be more aggressive and their pci placement if they have that. I'm rarely in a spot where I need to take a pitcher out because their pitch counts are so low.