So I've been thinking about this, and I wonder, why is it so hard to find an appropriate name for the class that doesn't imply rank? Should we even try, or should we just say "No, this is about having a type of authority/control over the party" and embrace that?
(Being slightly devils-advocate-y with my phrasing, I admit!)
Can I take a third option?
As it is, in D&D, we have several names that have been "grandfathered in," despite having only a weak association with the intended concept. "Cleric," for example, is a word still in use today, and even has some set phrases which have nothing to do with religion (e.g. "clerical error.") "Barbarian" is a huge no-no word in modern English; you'd only use it if your intent was specifically to insult another person's culture, and insulting a person's culture is seen as a wholly inappropriate thing to do, even by accident. Both "Druid" and "Bard" specifically single out a particular Earth culture, and "Ranger" singles out a single author's work. Etc.
Thus, I think the problem is more that, with the Warlord, it hasn't yet developed the patina of use that the other words have. It hasn't built up a protective layer of familiarity to cause people to forgive its foibles and accept that the two uses of the word (modern-day and D&D-only) are separate things, which only partially overlap.
Of course, the natural rebuttal at this point would be the Warlock--but it's actually not new, it was a level-title for AD&D Wizards (8th level) as was Sorcerer (9th level). And it's not like "Warlord" is never used in fiction, fantasy or otherwise. (In fact, a series I love quite a bit, the
Black Jewels books, uses "warlord" as the general title for all male members of the Blood, people who can do magic, regardless of their social station or the strength of their magic.) So, again, I think the issue is really just that people aren't comfortable with the word, and thus seek to remove it or find something that will be comfortable--but they're almost certainly not going to succeed, just like how trying to replace all of the standard D&D class names would leave most people struggling to find good ones.
If you had to throw out all the traditional words, e.g. not just "Bard" but also "Minstrel," not just "Fighter" but also "Warrior," wouldn't most of the alternatives feel uncomfortable, confining, limiting? Yet if "Bards" had always been known, originally, as
Gleemen or
Troubadours, would we not be in exactly the reverse position? If "Druids" had always been known as
Wardens or
Keepers, wouldn't "Druid" be seen as an inappropriate attempt to pigeonhole the class into a single culture's beliefs? If "Fighters" had always been known as, say,
Pugilists, might not "Fighter" be seen as an incredibly bland word, discarding all the rich meaning of the name for something that describes
anyone who gets into combat?
"Warlord" is just a name that bothers people because it hasn't aged as much as the other names have. In another 30 years--and 3-6 more editions of D&D, I'm sure--I suspect much of the resistance to the name will have disappeared, and we'll be all upset about whatever is the
newest new class on the block, probably "cyphers" or "somnambulists" or something like that.
TL;DR: "Why is it so hard to find a name for Druid that doesn't specifically reference Celts? Why is it so hard to find a name for Barbarian that doesn't imply being uncivilized and/or Norse?"