Plant is not good enough to expose Bute lack of heart (at least in his prime, cause he showed some heart in his later years).
Yeah, I think the most logical outcome is Plant having an edge early due to his quicker feet, but steadily Plant's inability to keep Bute off of him would lead to Bute's power breaking Caleb down. Bute TKO 11 via a body shot or a left uppercut.