The way we've been designing the leadership features in the Warlording the Fighter thread, is that the other characters are under no requirement to do what the Warlord directs. However, if they don't, then the group does not gain the benefits that would result. In fact, if the Warlord can't inspire their group to follow their directions, it's the Warlord that's penalized through loss of their actions.
Though the argument could be made that the group also suffers if the Warlord loses their actions - but that's what happens with bad or failed leadership - lack of synergy.
So as the fighter or wizard, or whomever, I can choose to invalidate the warlord's action by not doing as "ordered". Who's the jerk there? Now I'm blocking. And that's not fun for anyone.
Here's one I've used before on the WotC forum when this same debate reared its ugly head:
I used to play in a friend's homebrew, episodic WWII TTRPG game. Based on the character creation process, everyone was assigned a rank. Highest rank was in command for the mission (as would be expected for any kind of military action).
Here's the thing. Player agency was kept intact because it was presumed to be roleplayed such that the commander of the mission ordered the action the other players
chose to take. We use to call it "Shrodinger's Command". What did the lieutenant just order the private on the 50-cal to do? Whatever the player of the private on the 50-cal decided to do.
Player 1 [Private Heavygun McNally]: "I spin the 50-cal around to shoot those Germans on the mezzanine!"
Player 2 [Lieutenant Snappypants]: "Private! Look out for those krauts up there. Take 'em out!"
GM: "Cool. Okay, Player 1, make your roll to light them up."
Why can't roleplaying leadership type actions in 5e work the same? Why do you need crunch to justify something like this? Heck, without crunch you have more freedom to play it to whatever degree you want without having limitations like rules getting in the way or quantifying and restricting you.