I think this might be slightly incorrect: if at least a quorum of nodes is alive and there is a leader (which isn't always the case), there's at most one leader, and at least a quorum of nodes minus one (the leader), is in `Follower` state following this leader.
Any other running node not within this quorum could be following some other node (which is no longer leader), it could be a candidate, or  if I'm not mistaken it could even be a leader for some lower term (yet won't ever be able to reach consensus on anything).