Patur Aval Assur,
I’ll try to take another stab at this discussion without tying myself up in rhetorical knots like last time.
Would you do something if you received no benefit whatsoever?
I don’t think this is possible. The definition of an action (doing) is something that causes a change – and any change is either beneficial, harmful, or both.
Benefit includes physical reward, getting a good feeling, earning schar, etc.
I think there is an error in this premise that is at fault for creating what may be an artificial conundrum. You seem to assume that ??? encompasses all benefit, and that actions for the sake of ??? are separate from actions for benefit. I do not think Chazal intended those definitions.
I think ??? is a benefit that is not ???. Why is ??? a benefit? Because it reveals our purpose. Why does our purpose have value? Because we are hardwired to desire our purpose.