Well, my suggestion was that rather than have A single warlord class, there could be like three prestige classes. Set the bar fairly low (3rd level, Int 13, Cha 13, History proficiency) but have the three classes focus on different aspects (effectively, acting like mini subclasses).
1.) A healer/inspirer/cleric replacer
2.) A straightforward buffer
3.) A maneuvers and action granter
This has the advantage of allowing the DM to pick which types of warlords he'd allow in his game. He might be fine with buffs and actions, but ban inspiring healing, for example. Rather than ban the whole warlord class, he just bans the healer PrC. Similarly, it could allow the PCs to custom tailor his warlord (focusing on buffs, but ignoring maneuvers) or bounce between them as they want to get some features from both. Lastly, the 3rd level limit (on par with when most classes get a subclass) can be used to eliminate the "neophyte, wet-behind-the-ears 1st level PC being a combat leader" problem. As an extra bonus, it doesn't need to use the warlord name either; for those who find it distasteful.
Hmmmm, lets contrast two approaches here, just to see where this really goes...
The 'base class' approach would have a warlord class as a primary class with presumably 3 level 3 subclass options.
The PrC approach would have 3 PrCs, enterable at level 3, which would each pretty much recapitulate the subclass options above.
The base class approach IMHO has the advantage of being something you can pick as your character's archetype. I could be the young King Arthur for instance, or just starting out as an officer, non-com, etc. Inexperience doesn't exclude one from being in a leadership position or acting as some sort of leader, so there's certainly a viable concept there.
You can still MC into this class of course, but you'll have to take 3 levels to get to the 'good stuff'. OTOH there may well be base class features worth having at level 1.
With the PrCs you're going to have to recapitulate the base aspects of 'being a warlord' 3 times, or else the entirety of your shtick is ONLY one feature? That's possible, but why would this as the only alternative be a superior design choice?
In all I'm just not seeing what PRCs gain you, aside from the people that just hate warlords get to say out of the side of their mouths "there isn't REALLY a warlord class, see, we were right!" which IMHO isn't really a design goal, even if it will please someone somewhere.
Honestly, I'm not saying I think that a PRC warlord would be all bad. The one advantage that PRCs could have, in principle, is some freedom from usual class progressions. As with the Rune Scribe, a small number of levels could compress a lot of advancement into them, with the proviso that the power range can't be much more than what would be true for any other 5 level advancement.
Honestly, I almost think PRCs are a bad idea as envisaged. I'd rather see some sort of 'overlay', more like the 4e Theme design, where instead of advancing in a different class, you just get appropriate power/feature/spell/whatever choices at specific levels based on membership in the 'PRC'. That allows the design to accommodate something where it can have say a level 17 or level 20 'capstone' that is really impressive, instead of just kind of petering out after 5 levels like Rune Scribe does. Now, admittedly, a designer could simply provide better runes at high levels and make more of that specific design, but I doubt the same would be true of a warlord PRC, it would have to contain heavy scaling within all of its features in order to remain a relevant part of the character. If instead you simply got more extra cool stuff at higher levels and continued to advance in your regular class, it would be a bit nicer conceptually.
The problem of course is that such an 'overlay' is virtually bound to be a power up. Since 5e has unfortunately eschewed any sort of common resource use framework it can't do what 4e did and make an overlay that offers power swaps (even 4e themes are at some level power ups, admittedly, but they COULD have been designed not to be). So, we're probably boxed into PRCs that have to either advance fully to level 20, provide some sort of additional scaling mechanic, or simply become largely irrelevant after a few levels.