Epicurus responds that Pleasure can be perfect (in removing all pain, often thought the neutral state) and afterwards admits only variation. Just as the Stoic sage may vary in different qualities (rich/poor, young/old, Greek/Non-Greek), but not be more wise, pleasure varies in state to state (Joy/Tranquility), but not be more perfect.
I agree withj wbernys here and this is why I would say that once you focus on the logic implications of the foundattional premise that there are only two feelings, it makes perfect sense that the best state is going to be one of pure pleasure accompanied by no pain. Such a goal serves as a target to emulate and aspire to, just as the Epicurean theory of gods provides that target of what the best life would be -- which is much as is stated by Torquatus in the line we quote often:
[40] XII. Again, the truth that pleasure is the supreme good can be most easily apprehended from the following consideration. Let us imagine an individual in the enjoyment of pleasures great, numerous and constant, both mental and bodily, with no pain to thwart or threaten them; I ask what circumstances can we describe as more excellent than these or more desirable? A man whose circumstances are such must needs possess, as well as other things, a robust mind subject to no fear of death or pain, because death is apart from sensation, and pain when lasting is usually slight, when oppressive is of short duration, so that its temporariness reconciles us to its intensity, and its slightness to its continuance.
[41] When in addition we suppose that such a man is in no awe of the influence of the gods, and does not allow his past pleasures to slip away, but takes delight in constantly recalling them, what circumstance is it possible to add to these, to make his condition better?
Which answers the question:
... there being no mystery to setting out total absence of pain / perfect pleasure as the theoretical goal, as that conclusion is clearly and logically compelled by the two feelings doctrine, in the same way that the observation that everything in the universe is ultimately composed of bodies and space rules out the presence of supernatural gods.
The difficulty is not that this two-feelings doctrine is unclear. Cicero allows Torquatus to spell it out plainly, Diogenes of Laertius cites it clearly, it is embedded into the fabric of much core Epicurean doctrine. Every ancient student of Epicurus would be expected to know it. The difficulty is that since the suppression of the school, and as part of that project, anti-Epicureans have been trying to make Epicurus into a Stoic and reconcile him with mainstream Greek philosophy by placing an attitude / single feeling (tranquility) as the ultimate goal of life. This deprecates pleasure into a tool which is to be discarded as soon the unthreatening goal of absence of pain is achieved.
If one focuses on the very clear big picture it is obvious that the theoretical best life is one composed solely of pleasures with no presence of pain. Epicurus knew that we as mortals can't reach that state, just as he could not cure his kidney disease, but the essential thing for a philosophy to do is to set forth the goal - the target to which we aspire. "Pleasure" - complete and unadulterated, but not specific in kind, as we are individuals - is the goal. This perspective answers those who like Plato in Philebus or Seneca assert that those who hold to "additive theories of pleasure" are being illogical. It's no harder for an Epicurean to deal with the difficulties of reaching pure pleasure than it is for a Stoic or Platonist to deal with he difficulties of reaching pure virtue. And in fact it's a whole lot easier, because pleasure actually exists, and Platonic ideals and Supernatural gods don't.