I don't know how best to describe this, but our current GM is having a more open ended game than normal, which I am not disliking, but just note we aren't using an AP or module.
In the moment I'm having fun (minus botched dice rolls and bad communication), but it feels afterwards during the week like I'm second guessing my character choices (feats and abilities, not tactics used) and that I'd be better off with a different class entirely.
I feel like the current party dynamic is working well, but I feel semi-useless, even being the major factor in a fight. I'm not sure if the newness and magic of Pathfinder is finally wearing off, but nearly every week I see myself thinking I'd be better off as literally anything else.
I'm playing a warder (path of war) "abusing" reach and attacks of opportunity. Other party members are an Armorist (Spheres of power third party) and a Spheres of Power witch.
Armorist is good at damage and intimidation.
Witch mainly uses nature magic for utility or summons golems for offense/defense.
What specifically do you need help with, and what specifically happened to that made you feel this way?
If AoOs are hard to come by - it's the best idea I can get from your description - then you might need more mobility, or maneuvers which don't depend on AoOs. You should be able to get these and retrain other maneuvers as you level up. Vague, but then so's the description.
I've played in campaigns like this, where I have fun in the sessions but then feel kind of empty afterwards because there's no ongoing story development to make it feel "worthwhile." The best I can compare it to is television in the 1950s to 1980s, where every episode was meant to standalone and be viewed in any order (exceptions: soap operas and a few other genres). The rise of long-form narrative TV in the 1990s and later is far more satisfying to many viewers, with even comedies like The Good Place embracing a "meta-story" along with the laughs. Adventure paths give a feel that "something is happening" and that "it matters" because you feel like you're moving toward an epic conclusion.
If it's that you don't have a connection to an ongoing plot (as Jhaeman suggests) then you need to decide on a goal and pursue it actively. Become a ruler, free all the slaves, found a mercenary company, whatever.