Would the Prometheus class be a heavy cruiser rather than a battleship?
Short answerIt is closer to a battlecruiser because one warship can divide into three cruiser-sized combat elements.
NotesThe Prometheus is judged by combat function rather than by Starfleet's official terminology. Its defining feature is the ability to separate into three cruiser-sized fighting elements, concentrating unusual offensive flexibility in one hull. That capability places it closer to a battlecruiser than to an ordinary heavy cruiser. Fictional systems can still be mapped to naval roles when their effect on combat is clear.