Sure, but I have no problem with a "fifth-wheel" character being better at fifth-wheeling than other options. Being the best option for a subset of all party configurations is hardly the same as being the best overall class, period.
Eh, but he isn't just the best at "fifth-wheeling" if he can grant an action for an action... he's the best at maximizing effectiveness period which means a party with a Warlord is going to be significantly stronger and more effective than a party without one.
It's hardly silly, it's one of the main examples of why the action granting isn't overpowered. Casting a high-level spell is, on a per action basis, the strongest option in the game.
In a general sense yes... in a more nuanced sense it's the strongest option of the game as long as there isn't a lower level spell or lower cost ability that would accomplish the same thing.
That's why high-level spells are so resource limited. Any high-level spell is only going to happen once per long rest per high level caster. With a warlord in the party, that frequency doesn't change. The only change is that it could happen on the Warlord's turn instead of the caster's turn.
Well in the sense that a high-level spell is the ONLY option that will achieve the desired effect yes... in actual play though how often is a second wish spell necessary as opposed to a lower spell effect? The point is that in being able to trade his action for the most optimal action (not necessarily the highest spell available) the Warlord does in fact have the most powerful ability (in a general sense) of the party.
Do we need healing this round... the Warlord can do it, Do we need to stop that trap before the next round... the Warlord can do it, DO we need the Barbarian's damage output on a BBEG... the Warlord can do it. Do we need a teleportation spell to get us out of here before someone drops... the Warlord can do it. Yes there are resources to be managed but that's there irregardless of whether the Warlord is a part of the party or not. What he does is make it possible to bring to bear the best ability (given resources are being managed by all characters) in any specific situation. That is a really powerful ability and would change the effectiveness of a party by a significant amount if played properly
Only with 3+ casters in the party would the diversity of spell options available on the Warlord's action overcome the inherit weakness of not playing a caster that provides a broader pool of spells available to the party as well as the spell slot resources to cast them. And I'm OK with an action granting class being a superior enabler in a diverse party.
Again I'm not sure I agree (and since there are a majority of caster classes it's not unreasonable to think there will be 3 in a party of 5 or more characters)... being able to cast the right spell... or in fact use the right ability when necessary to save a spell slot from being expended is a powerful ability and a game changer. I'm not sure it's as powerful as having spells to waste (of course if you don't need them or they are overkill for the situation I could see the argument) but it's probably one of the strongest abilities in the game because of the sheer versatility it brings to any situation.
The only one there that concerns me is sneak attack, or access to Sharpshooter/GWM level at-wills. All the other options are resource constrained already.
Eh, the fighter getting another go at an attack action that grants 3-4 attack at high level is nothing to sneeze at either. But again it's the fact that this Warlord can bring to bear exactly what is needed (as opposed to other classes having to sometimes improvise when it's their turn and they don't have the exact ability necessary to optimize their response to the challenge thus resulting in reduced effectiveness and/or wasting of some resources) that is the true power of this ability.
All that being said, I'm spitballing based on a hypothetical class with only one feature, the ability to give their action to another character to take. Such a class would be strong, scaling with the number of other characters in the party as well as the optimization level of those characters, but not OP. A real warlord class, though has a limited subset of the options that would be granted by that hypothetical ability, but granted their own set of warlord abilities as a trade-off.
I think depending on the optimization levels of the other players, what options (such as feats, magic items, etc.) are allowed, this hypothetical class could be not just strong but quite overpowered. I think being able to bring the most optimized ability to bear (given cost and effect) on a 1:1 basis is a much stronger contribution that many realize.