Yeah, I don't like Warlord, but the alternatives are worse.
I like Champion, but I think that name is being reserved for 'Champion of X, Y, or Z.'
Commander or Captain implies that the character is in charge of the group. I know he fills a leader role, but I bet WotC is trying to make it so that a character can fill that role without automatically being the 'in charge player.'
Maybe Fighters should be fighters and Warlords should be Warriors. The difference being that a fighter concentrates on personal fighting skill, while a warrior is one that learns to fight and think as part of a group.
I think that would work:
Fighter
Warrior
Ranger
Paladin