I mean it as a real consideration towards what a class is in 5e. Ignoring it means you're fighting against the core concepts of the edition.
Is there a Class Designer's guide somewhere that spells that out? Is so, link it. If not, don't pretend that there's anything so bizarre as a requirement for single-player or single-class party viability in an essentially cooperative game that runs on spotlight balance.
That's OK, then. If it isn't a bar to the consideration of a class for inclusion, then it only has bearing on the later design phase.
If the DM is strictly following the rules for encounter building and daily xp, I don't see a single class (or really even a single subclass) that would have difficulty making it through adventuring days.
I know 5e has a rep for being 'too easy,' but if you do follow those guidelines, you'll end up with 6-8 medium/hard encounters (by including some encounters where the party is outnumbered, resulting in hard encounters with less-than-hard exp value), and single class parties will likely choke on that, especially indifferently optimized ones at 1st level. Some of the more versatile classes, though, you could optimize a party of them to cover everything it needs, and, if you heavily optimize a single-class party it could probably blow it's way through at least a full day of standard encounters, even if they're all hard.
But, honestly, that's going beyond the viability of the class to the manipulation of the system.
Again, it's one of the hidden design goals of 5e
If it's hidden, you can't claim it as a goal, it could just be a fantasy of your own.
This hits on another design goal and one that was first done successfully in 4e. That every class be fun to play at every level. No more Fighters are great for the first 10 levels and Wizards rule the last 10. Same should be true for a full Warlord class.
No reason it shouldn't hit that imaginary design goal, with a full class, either. The sub-class in question doesn't even start to boot up until 3rd, of course, because it's a sub-class. :shrug:
They may be silly to you, but it is what 5e is.
Again, that is a baseless assertion. You'll need to find it in print, or get a designer to swear to it, before I even start to take you seriously.
I mean, Mearls /is/ on record with goals for 5e's inclusiveness and integration of all past editions to the point different players could enjoy the 'styles' of different editions, at the same table. No one takes that seriously.
Does it put limitations on what a Warlord can be in 5e?
No, only on how design might be approached.
For a full class, I'd start with what he is doing there and then figure out how to flesh that out with a full class design that keeps in mind what a 5e class is. Build the full class in the reverse way that the Arcane Trickster or Eldrich Knight was built.
Nod. I can see that as a development path, too. Treat this class as a faux-MC sub-class like the EK or AT is a faux-Wizard-MC for their native classes, and extrapolate the full class from that.