Yes and no...I think the biggest drawback to the Warlord making it to 5e is that no setting requires it. Eberron and the artificer and Dark Sun and the psion are linked in such a way you really can't do the setting without that class. I don't think Warlord is linked enough to any setting (maybe Nentir Vale?) enough for them to say "we need a new class for this setting or fans are gonna riot" Though who knows.
Birthright would be a amazing setting for the Warlord/Marshal. But also: Adding a class to a book that is otherwise largely DM-Exclusive in it's design encourages players to buy it, expanding the target audience for that book which increases sales beyond just the DMs who aren't designing their own settings, or who do and just wanna pick up the setting for another reason.