Military units go as small as four, and this is a DM-heavy board. A leader makes for a great NPC. A leader who leads entire cities or armies makes for a very compelling and dangerous NPC.
A D&D party isn't a military unit.
The other PCs are not the "warlord's" subordinates.
There is no war, no army, no nation, no battlefield - unless the campaign explicitly goes there. The warlord neither fights in a war, nor is he a lord of anything.
Worst of all, this "class" affects the archetypes of other, actually legitimate-in-a-D&D-party archetypes. Your fighter is an independent type? Too bad, someone else took "warlord", so now you're an implied mook. Brings a whole new meaning to the warlord using some random ability which involves ordering about his "friends" with some "Feather Me Yon Oaf" bollocks, and the paladin turning around and saying, "Oh yeah? Who's going to make me? You and which army?"
Which says it all really, because the "warlord" should be in an army, not in an adventuring party.
I'm happy to be proved wrong, but that's what it's looking like from here. It's looking like some marketing stunt for the miniatures game, based on a bunch of crunch abilities, archetype gone out to lunch.
makes for a very compelling and dangerous NPC.
You said it. An orc warlord fits, even the name fits - he fights wars and has underlings. As a PC class, it doesn't belong in the core.