I'm rethinking that, I don't see an is/ought problem here.
Living beings pursue pleasure and avoid pain.
Epicurus does, to my perspective, state this as an observation of the way things are. A fact of nature.
He is not saying we ought to follow pleasure. To my mind, he's saying we do. Living beings do. What he is doing is calling us to do this deliberately, to understand how to do what naturally comes to us in a deliberate, thoughtful, rational way instead of second-guessing or obfuscating or rationalizing (in a negative sense). If the natural goal of life is ultimately seeking pleasure, do it, lean into it, don't fight against the current, don't shake your fist at the sky, don't blame the gods, and so on. He sees no need to "prove" pleasure is the goal anymore than snow is white and fire is hot. Those analogies are important. Pleasure is the telos is akin to fire is hot. You can stick your hand in the fire and maintain it's not hot, but you're still getting burned. Likewise, you can claim to be following the path of virtue but you're still doing it because it gives you positive feelings to be doing it.