I am generally opposed to the proliferation of classes. I played AD&D for about a decade and the only class added in that time was the Psionicist, which had a unique niche that justified its creation. (I'm not counting the Gladiator because it was Darksun-specific.)
If one of my players wanted a Ninja class, I would point out to him that the 5E way of modelling a Ninja is a Shadow Monk. If you want to play a tactical fighter with tricky maneuvers, that would be either a high-Int fighter (of any type) who cleverly uses tactical options like Push and Disarm, or if you want built-in support for your concept it would be a Battlemaster.
There are Warlord-inspired variants that I kind of like (Steeldragons' Warlord on these forums, which is basically suited for leading large numbers of lesser creatures like hirelings and minions), but I still voted No on general principles. My mind could be changed if it were shown that the Tactician-or-whatever-you-call-it were bringing some unique value to the table that justified the increase in complexity from adding another class to the game, but my default is No.