OH! Well that's simple. It is systematically "just different" from other class ideas because it was created, quite literally, to follow/fill a systematic class grid that was completely artificial and developed for a different game.
Again, to be clear, that's not 4e bashing. That is just simple fact. Exactly what it was created for. They needed a "martial" "leader" to fit into their little boxes and said..."How 'bout this guy?"
So, yes. The warlord is "just different systematically" and, thus, does not fit/work to include in a non- class "role"/power source grid organization. 5e is not such a system.
I guess we're all done here then.

That was easy. Someone shoulda just asked that on page 1.