A colonel leading from the front does not mean he is necessarily doing the job of a captain or a lieutenant. Sometimes the colonel, with his greater experience and wider battlefield responsibilities, may see an opportunity that his subordinates can't see and it's simply more expeditious for the colonel to provide direct control. The captains and lieutenants will still be leading their companies and platoons. There are plenty of examples of senior leaders leading from the front...and it can pay off, providing the leader isn't killed.