IF someone was to do a write up of a "Warlord", my biggest hang-ups with the class is that, at it's core, it feels like the designers are saying "Fighters are master at fighting, battle and war!...well, sort of. The actually don't really know anything about tactics or maneuvers or, uh, fighting tricks...Warlords do because Warlords are the only ones who can use tactics, maneuvers and other fighting-tricks to 'fight'." That's how it feels to me.
To an extent, the Warlord, Rogue, Ranger, Cavalier, Barbarian, Duelist, Thief, Monk, Assassin, Bandit, Pirate, Swashbuckler, Archer, Knight, Scout, and quite a few other classes, sub-classes, attempted classes, speculative class ideas, PrCs, variants, and whatnot (heck whole 'fantasy heartbreaker' game systems) over the years, have all stemmed from the marked inadequacy of the traditional D&D fighter.
5e chose not to address that issue by vastly broadening the Fighter class, so here we are.
So, a "warlord", IMHO, should come along with an optional set of combat rules for such "tactics" that anyone can attempt.
This has been a problem that's kept the fighter in the dog house so much of the time. Propose something remotely cool/interesting/useful/effective for the fighter, and you get a refrain of 'well everyone should be able to do that,' followed by the conclusion that, 'well, gee, everyone does that, so it's not really adding anything to the game but complexity,' and *snip* gone. See, for instance, virtually everything they tried giving the fighter in the Next playtest, but, particularly, Martial Damage Dice.
Once those were implemented into the core rules, a Warlord could have abilities that simply made it 'better' at doing those. I'd remove any "damage/combat" oriented abilities that directly involve the Warlord.... he isn't trained to go toe-to-toe with enemies, he's trained to sit on his horse at the top of a hill and direct the armies under his command. Intelligence and Wisdom (or maybe Charisma) should be his two 'stats', his HD should be d8, extra attacks as a Bard. No spells or "magic powers". Everything should be mundane and focused on using intellect and experience to direct others...not himself.
Something like that I could get behind. Alas, I don't think many Warlord fans are going for that sort of interpretation.
It's certainly within the range of concepts the Warlord could reasonably be expected to cover.
But, no, bundling the Warlord with a large set of variants isn't a great idea. Options modules should be, well, modular. If you want just the warlord, you opt into just the Warlord. If you want just some battlesystem-esque battlefield rules, you pull in just those. Modular.
That's me objecting as a 5e fan, BTW, just to be clear. I'm more sanguine about it thinking strictly as a warlord fan, though it'd have to be part of a general system re-design to really work.
A difrent out of the box re-imagining of the warlord might be as a pet class.
so he would come with some soldiers he has comand of, and those got bonuses for things like forming a shoeld wal and other players could chose to be part of that formation.
Not much of a stretch, and given 5e's more open design, bounded accuracy, and treatment of 'pet' classes, animating undead, and the like, I'd have to think something like that would be almost inevitable. Hopefully, it'd be kept as an option, a matter of customization or other player choices, as it certainly wouldn't be for everyone, nor every table.