I don't think anyone asked what is the definition of a midlength. It really doesn't matter. It's like discussing what a Fish is. I'm sure I have a different idea of what a Fish is, then many on here. You could just measure cocks, that works too. So, getting back to the OP question:
Is it possible to rip on a mid-length?
I personally think ripping is too subjective of a word. Everyone has a different thought on it, and a lot of it has to do with a million different variables. I started surfing in the early/mid 80's. When I think of ripping, I'm thinking of someone surfing well on a HP shortboard, mainly because thats all we rode back then. If you rode anything else, you were super old (like 30!) Surfing top to bottom, hitting the lip vertical, single carving cutbacks with close to vertical rebounds. This may not be what others consider ripping, but that's still ingrained into my thick skull from my younger days. Do I think Devon Howard surfs well? Do I appreciate watching him? Hell yeah, he surfs great. Is he ripping. Not to me. But, that's OK. He surfs with flow and incredible style, and that, I appreciate more than ripping. I don't expect when people aren't riding an HP shortboard to rip. I actually think it looks pretty dumb when people are trying to smack the lip vertically or surf off the tail on a midlength or longboard. My theory was always, if you are going to hit the lip, then do it on a shortboard. Does that take anything away from any other type of surfing. Not at all. I appreciate the lines some people draw on bigger boards. I love riding logs and noseriding. Nice big carves on a Fish. All boards can be fun, and honestly nobody should care what I think anyway. If you are having fun hitting the lip on a longboard, and it doesn't cause harm to anyone else, then by all means, you go for it (but it does look kinda dumb)!