Jester David
Hero
4e was an edition a LOT less concerned about flavour and tonal overlap though. You had the warlord steal the thunder of the bard (and their place in the PHB1), you had the invoker that was basically a wizard... of the gods, the avenger that was basically a holy rogue, the runepriest that was a dwarven cleric, the seeker than was a magical ranger, the swordmage was a wizard that good at surviving melee. Etcetera, etchetera, etcetera.Bards and Warlords coexisted in 4e just fine. I'm not sure why they wouldn't be able to in 5e.
The sneakiest character in the game should be the rogue. The smartest character in the game should be the wizard. The toughest character in the game should be a barbarian. The character best in the wilds should be the ranger. The character best at fighting should be the fighter. Etc. Every class has something it should be the best at. It's wheelhouse.
The problem in 5e is that the bard, by it's nature, doesn't do a lot of unique things. It's always been a rogue/wizard with a minstrel feel (with a dash of fighter). So it does roguey things and wizardy things. The one unique thing it does is inspire people. (Which is already a feat.) But it should be the best at inspiring people.
So what is the warlord best at? It can't be inspiring people then. So if the design focuses on that, it's making a character that can never be the best at its role. Like a new class that's a less sneaky rogue or a barbarian that isn't as angry. Otherwise, again, it's a class making another class irrelevant.
Ideally, the design of the class should be flexible enough that you could make Charisma your second or third highest Ability Score and still be inspiring if you chose.
And instead of being the best at inspiring people, the warlord could be the best at directing people. The best at tactics and strategy. The best at commanding people.