And I disagree that there is (or can be) some non-contextual definition of “happiness” that can be applied except in the most abstract of cases.
Which leads to the question: Do we stop trying, or do we simply define our terms as we think best, such as "believe that a god is a living being blessed and imperishable" or "by pleasure we mean the absence of pain."
I think Epicurus is with you, and that he therefore - rather than give up or give in to false presumptions - determined that he was going to state his own terms to explain the answer to contentious questions.
I therefore think Dons "subjective wellbeing" helps explain the issue, but in Epicurean terms Epicurus decided the best term for this either is or falls under "pleasure."