Tier 3, but very strong ones.
Path of War isn’t handing out game-warping effects like open-topic divinations, long-distance teleportation, or poaching monster abilities via conjuration or domination. The hallmarks of Tier 2 and above simply aren’t present.
But among Tier 3 classes, Path of War initiators stand out. Several of them have extremely potent defenses, that can be very difficult to breach, and almost all of them have top-tier damage-dealing ability without breaking a sweat. Because they were designed to be strong “out of the box,” so to speak, because a design goal was to make them good even when played by naive newbies, when you start optimizing your feat and item choices, they can get really monstrous. And several maneuvers were overtuned—there’s nothing outright broken as far as I know, but there are definitely things that are simply more powerful than they should be at the level they’re obtained.
Trying to break things down within a tier is often an exercise in frustration and argument, because the tiers are already broken up by the more distinct dividing lines. Anything within a tier is going to necessarily have to start getting into more nebulous distinctions. But I will say that, if I recall correctly, the warder and zealot have a reputation for being the most problematically strong of the Path of War initiators.