I'm kinda lost now, I've forgotten what if anything was in dispute or I didn't understand.
I agree with what you've said (except for being able to imagine a non-causal world) but/and none of that goes towards suggesting that causation is not/is other to (only) conventional, right?
hmm, not sure. Are you saying that even were I to arrive at a non-causal understanding of the world I could only get there through having a causal understanding in the first place?
But none of that speaks to whether it's 'true' or 'real' or anything, just that it's useful, as it undeniably is (as is our perception of time as linear, which is a pretty closely related thing).
Something being useful doesn't debar something contrary to it also being useful (or from existing). We think of the world as flat and lots of our activities rely on us thinking it is so but that doesn't mean that it's not sometimes useful to think of the world as round or that thinking of the world as round prevents those flat-world activities and none of that has a bearing on which if either are true.