Almost everything from the first Path of War, has been implemented into Hero Lab, through the Community Package.
Bits and pieces of the second book, Path of War: Expanded, have appeared. Not everything from the second book has been implemented, for example there are new disciplines which the new classes each have a couple to a few of, and the existing classes get to pick one of a specific set of the two new disciplines per existing (first book) PoW class.
There are feats (Martial Training), which allow some of the PoW:E disciplines to be picked as per the feat, but not all of them.
Those disciplines that are implemented for the new book (most) are not assigned to the existing classes at all, and not entirely to the new classes either (some have partial choices, one had full choices and one had only a single discipline the last I checked).
You can grant a character an extra feat (additional feat, via ShadowChemosh Adjustments) that they don't actually take, and then grant them the discipline that they're supposed to have access to (for the ones which are implemented via the feat route), and then take them... so you can play around with PoW:E to get a lot of it in, even if not all of it is included in the package.
Doing it that way is kind of an ugly approach, but if you have a player who really wants PoW and PoW:E stuff, you can make a lot of it work.
If you were to stick to the plain Path of War (original book), just about everything is included.
The classes (Stalker, Warder, Warlord) are a fair bit stronger than non PoW classes, but casters are still a lot stronger in combat, and outside of combat situations still have a lot to do which pretty much none of the martials are even close to.
Essentially, if you allow PoW material, any martial that doesn't go that route, is substantially weaker than any who do... not saying that's a bad thing necessarily, as it partially closes the gap between martials and casters.