Path of War is amaaaaaazinngggg! You'll notice your melee initiators doing some pretty incredible damage between levels 1-5. These are the levels that melees normally always shine though, except the martials will definitely blow the classic Fighter, Paladin, Barbarian, and Ranger classes away.
Levels above 5, however, the PoW classes will start to slink behind your typical 4th levels spells. Being able to summon a Tiger or Satyr with Summon Nature's Ally 4 is pretty hard to beat.
So yeah, your melees will be doing lots more damage and have lots more options at their disposal. Game breaking? Hardly.
I've re-read one of the rules in the System Use and am inclined to agree that all the initiator classes DO indeed get to swap maneuvers even if they take a class in something else.
"Retraining: Initiators can retrain their known maneuvers and stances; this retraining takes 2 days per level of the new maneuver and requires a trainer who can initiate the desired maneuver or enter the desired stance. The new maneuver or stance must be part of the initiator’s available disciplines for the class, and must be of an equal or lower level to the maneuver or stance it replaces. Note that this is unrelated to the ability of initiators to swap maneuvers for higher-level ones at certain initiator levels; that swap represents the initiator’s evolving style of combat, does not require a trainer, cannot replace stances, and can happen only once at a given level."
The fact that they mention the statement in bold can only mean it's referring to a multi-class initiator whom had their ability "proc" from multiple initiator classes at once, which can only be possible if the ability did indeed "proc" from taking a class other than the base initiator class.