Warlord's were OP in 4e. The weren't obviously OP as in being able to sit down and list one thing they just blew everyone else out of the water at. It was the combination of things they could do that was so powerful.
1. They could heal almost as good as a pacifist cleric.
(They had feats and utility powers that were very impressive when it came to healing).
2. Once they had their encounter powers set up they could cause almost as much damage as a striker over the first 1-2 turns of combat.
(In 4e number of attacks was what put you atop the DPR and Nova charts. 4e Warlords enabled about as many attacks as some of the better strikers could in the first turn)
3. They almost ensured the party went first.
(Huge Bonus to initiative for the party)
4. They got to position allies at the start of the fight so they could pwn the enemies.
(You do 0 damage if you are out of range and it's almost always better to focus fire. Warlord's helped make sure both happened with precombat party movement)
Yes. 4e Warlords were OP.
Ultimately I'm sure WotC could make something that worked... but the real question is whether there is enough demand among those who play 5e for WotC to devote the resources to a warlord as opposed to other things for the game... Personally I am very meh on the warlord... I wouldn't object to one but it doesn't even rank in my top 10 things for 5e I want. But I guess there could be demand enough to justify the resources... and I just haven't seen it. Or maybe the addition of a Warlord is suddenly going to make all those who stayed with 4e convert to 5e... but I honestly doubt it.
Sorry, no. They were quite competitive leaders, but not OP. Sure, there was synergy, there, but synergy exists on both sides of the combo.
Attack-granting, for instance, is powerful if you have someone who does a lot of damage with the right kind of attack. So is just having a second guy who can hit that hard all by himself.
And the funny thing is, in the 4 years of 4e, no one who actually took the time to analyze the game ever made this argument either. All the actual 4e analysis of warlords placed them pretty solidly in the pack for power.
And the Commander's Strike isn't good enough for a proper Warlord. It's restrected, because it's given to an honest-to-gawd fully kitted Fighter.What's needed is an unrestricted ability, but one that is restricted by its own subsystem (such as spell slots, superiority dice or sorcery points)
Remember that the action economy degradation doesn't need to be only paid by the Warlord. I think the canonical example of this is the Battlemaster's Commander's Strike.
Battlemaster uses on attack (which may be only 1/2 or 1/3 of an action) to grant someone else an attack (which might be a full action for them and/or benefit from being on a different turn like the rogue). It also gives a boost to damage. The costs are the reaction from the receiver, which means that 4 warlords couldn't trigger the same rogue one after another, and it's using a limited-but-not-too-limited resource from the Battlemaster, a superiority die.
Now, from a design consideration, "pay now for someone to get something later" might also be considered a degradation. An example of that would be granting the equivalent of the Haste action. I think that's a valid concept to explore as well.
Well, considering it's been what, three years now since 5e has come out and we've seen consistent calls for a Warlord, I'd say that there is a fair bit of demand. The fact that someone posted some five or six different Warlords from the DMsGuild, some of which have gone best seller - silver and copper, I'd say that there is some demand.
And there, we are talking about people who spent all their free time analyzing 4e CharOp, with pretty much unassailable System Mastery. In some cases, people so into CharOp they had trouble seeing the game in any other terms, and talked about middle of the pack options as worthless trap options because they didn't multi-attack hard enough in round one.
And not one of them, ever, claimed that Warlords were too powerful. Even when someone claimed that Warlords were the strongest Leader, they got pages of arguments against the notion.
As in, it has its place in any Warlord-y character's toolbox, sure, but for the "real" Warlord, we expect more - we expect at least a few unrestricted action trades per rest.