Yep this. Even if the name of the class and even the entire class story are changed, having a support focused martial is a valid niche.This is not how 5E or D&D works in general, making it something I cannot feel concerned about. There are no such hard limits on sharing mechanics.
Game narrative is easy to come up with. We literally already had a warlord class in D&D. The class name is not terribly important.
And I'm not sure how warlord is invalid because other classes can be leaders. Could argue that sorcerer shouldn't be a class because other classes are casters.