As I mentioned I played through story on easy and it was no sweat at all. I went back and tried to change difficulty and it doesn’t look like that’s possible without starting a “new” story mode—you can’t have more than one and it resets your progress. That’s a little annoying that now I’ll have to re-level Raphael if I want to change the story mode difficulty.
But I did play the first couple levels on medium difficulty in arcade and that felt “right”, not too hard, not too easy.