I don’t have much experience with these subspecies and didn’t consider that. You could definitely be right, I don’t know. I’ll retract what I said before. I knew it was a Red-tail, and one of the interesting different subspecies, but beyond that I don’t know.
Most Rough-legged Hawks have a pretty dark belly or a very dark belly, so that can be ruled out. Agree with what you say about Ferruginous, adults also have dark leggings, and I’d think a juvenile would have a different back pattern.