I am sorry but, from the outside, both of these arguments look exactly the same, practically to a word.
People who don't particularly care about (Ninja/Warlord) telling fans of (Ninja/Warlord) That it is all right there, just needs some mixing together. People who want (Ninja/warlord) Saying that it really cannot be done, and it doesn't matter if (Shadow monk is labeled "Ninja"/PDK is labeled "Warlord"), it does not at all meet what they want out of (Ninja/Warlord).
Well, right from the start we reach an important point.
I do care about the inclusion of a ninja class. Not called that, necessarily, and not limited to just the Japanese Ninja concept, but rather a combination of it, the Assassin's Creed/4e Executioner style rooftop assassin, and a more modern fantasy shadow magic assassin. I've been beating that horse to death and beyond since the playtest, in point of fact. And I will continue to do so until it happens, or I lose interest in DnD, or a third party makes a really good one for me to use that my group unanimously has no objection to. Same with the warlord.
So, sure, that part is the same. It's the rest of it that is entirely different, as I enumerated above.
[MENTION=15700]Sacrosanct[/MENTION] I agree with most of what you're saying, except for the idea that you can do 90% of what the warlord should do in 5e. to be more specific, I don't think that you're looking at it from the right angle. IMO, to count as existing in the game meaningfully, you have to be able to "warlord" most of the time. Without houserules, homebrew, multiclassing, or feats. Ie, without the stuff a player can't reasonably assure themselves access to.
The ninja, you can.
The warlord, and I'd argue summoner, shaman, artificer (and with it, alchemist and tinkerer/inventor/engineer), mystic, and probably at least 1 or 2 other concepts that have been classes before and aren't now, you just can't.
You can warlord some of the time, but not most of the time. Most of the time, you are just another fighter, paladin, or rogue. Bard is the worst case, in some ways, because even when you are "warlording", you are really just Barding with a coat of paint over it and everyone agreeing to not notice the chanting and chicharones (I play a lot of DnD Online, where the Bard's low level components are Pork Rinds) as you pretend not to cast spells.
The monk base class abilities lend themselves so well to the ninja, IMO, that when you spend ki to jump to the top of a building, you are being a ninja, as long as ya do it stealthily.
To the idea that the ninja needs class features to be better at things covered by skills...I simply disagree with the basic premise. If it's covered by skills, the only requirement is that the class that used to have the ability to do it outside the skill system should have access to the skill that covers it in this edition. That's it.
Rogues don't need a class feature that makes them better than anyone else at thievery or disabling traps. They just need to be good at skills, because that specifically is part of the concept of the class, and have the skills that govern stealing and disabling traps. Which they do.
I'm not sure why it matters that pontoon shoes don't work IRL? Please explain how that is relevant? You want it to be possible in the game, or not? Ninja's should have a background that gives proficiency in ninja tools. I literally cannot fathom how that is even arguable. If we got a ninja full class, sure, they should also get proficiency in those tools. There is no need for them to be better with them than a rogue who takes the ninja background.
(although that does raise a system wide question of why rogues are better at skills that another class should be really good at, conceptually, and why Expertise isn't more specific, but also part of pretty much every class/how skills work for everyone.)
But a Bard with the criminal background and expertise Theives Tools is just as good at busting locks and disabling traps as a rogue. The thief rogue is faster, and the arcane trickster can do it from afar, but class to class, they're the same level of awesome trapmonkey.
Imo, that is exactly as it should be.
The difference is not objective. Whether or not you see a difference is mostly a matter of perspective.
From my perspective, a warlord is and always has been a type of fighter who is good at coordinating the troops. In every edition prior to 4E, the concept would have been covered by making a fighter, and just acting out the inspirational and tactical aspects. This is because the fighter is a very broad class, which covers every type of warrior that doesn't have magic. You don't need a specific class for warlord, any more than you need a specific class for samurai, because they're all just warriors who don't have magic.
It is objective. The warlord objectively cannot mechanically model the concept most of the time in play, while the ninja can.
What you describe about the fighter is also exactly why i think it is a class that is actively detrimental to the quality of the game. It isn't a class concept, it's a broad category of class concepts, and even then, it's a useless one.
Also, as [MENTION=6801209]mellored[/MENTION] said, the fighter in 5e doesn't do all those things.
If they fighter had been built to be what you describe, most of the meat of the class would live in the subclasses, instead of the core class. But that isn't the case. A Battlemaster is 80% or more "fighter", and 20% or so whatever concept you manage to beat out of the subclass.
maybe 70% generic fighter, 10% what you can get out of feats, and 20% subclass concept. Still very much mostly "fighter".
If the Fighter was a bare chassis, with most of it's features being in the subclasses, the Battlemaster might actually cover a warlord. But a class concept isn't covered if you can't spend most of your time doing it's "things", so no, the warlord isn't covered in 5e.
And yeah, I stand by my anti-fighter statements. It's been a terrible class in nearly every edition of dnd, and the game would be better off without it.