You have to understand, the language-game 'Philosophical Zombies' is above all a thought experiment. Whether we personally are not zombies, or whether zombies are possible, are not subject to assumption or observation - but, definition in this context. The thought experiment begins there, with looking to consequences if the definition is allowed to stand. So really, Dennett conducts a sleight-of-hand, which personally I don't think stands scrutiny, he just satssays what we call inner experience isn't really that, when clearly definitionally it is - a la cogitocogito.
P-Zombies is the parallel of the Turing Test, where gherethere is the recognition 'all we have' for other humans seems to be that we pass such a test of acting conscious, and so allows us to focus on the gap between our experience of ourselves and how we experience others, and examine our intuitions about ourselves and others.
This quote though points us at intersubjectivity. We do generally, if we are not solipsists, begin with the assumption other humans are like ourselves, and, that is functional and useful, in constructing our world and reality - like so: Indra's Net. That is, whether or not we consider other humans to 'really' be like ourselves, if we at least 'act' like they are, then we can engage in this peer-to-peer reality where our experiences are named and organised through engaging in language games, and we greatly extend our experiences and understanding by acting like other people are like ourselves - and, beliefs to the contrary aren't really functional. Through language tools like 'chunking' and assembling 'salience landscapes', and forming 'explanatory layers' that use those, we focus on the bits of the world where we can have influence, enabling our mental model of reality to give us 'cognitive grip' on our experiences. See detailed discussion here: According to the major theories of concepts, where do meanings come from?
I would explain the deep roots of this gap, between the idea of the Turing Test and the practice, by looking to how we expect a deeper mirroring by other humans: for them to deduce things about our experience by queues like wincing, and that the assumptions involved in that pre-exist our capacities to make sense of our experiences by naming them, involved in language. We just can't begin to sift noise for signal, and begin to form tractable models of the world, without accepting it. Babies isolated from interaction die, babies deprived of verbal language develop their own (babbling, hand gestures, etc), and risk never becoming fully cognitively developed if the don't get human interaction (see children raised by wolves, or severely neglected). Human brains fully developing, and language, arise together. An AGI could potentially arise out of language itself, in the way AlphaZero generated a chess player, this is likeI think comparable to how some twins sponteneously generate their own language from the evolutionary trigger of babbling (assiciatedassociated with FoxP2 genes, plus honed by mirror neurons).
I feel that the distinction in science between phenomena and theory, is a useful model for understanding the relation between personal experience (not private, but intersubjectively-informed) and language. Discussed here: Is scientific knowledge personal or general? We use tools like consilience and examining our cognitive biasees, to filter what about our experiences is intersubjective, and would be experienced by others in a similar way if they were in our situation.
We are enculturated into a peer-to-peer reality, but there is the capacity for a 'hard fork' or paradigm shift, if a new framing can take enough people into it's language game. This can help us understand the problems of interspecies communication.