I ask you, the experiencer, to describe and compare them. We do this literally every day in healthcare. We have rating scales for pain, for depression, for anxiety. Every single day, people experiencing these conscious states quantify them for us. And we can use those measurements to quantify how effective treatment is. And lo and behold, when people's quantifiable scores go down, they qualitatively report to us they are happier and satisfied with their treatment.
The fact that I can't literally experience your pain exactly as you experience it does not mean we have no ability to study it or systematically affect it. Again, we do this literally every day in medicine. And it works.
We learn socially how to label our emotions as children. We learn what happiness is, what sadness is, what anger is, etc. And our parents/guardians teach us this entirely through behavioral observation and modeling. They can't get in our heads any more than a scientist can. And yet, we all generally turn out to be able to ID our emotions. So we don't need to be able to access the "qualia" directly to be able to communicate and understand (and even empathize) with each other's inner lives.
You seem to be critiquing one particular version of materialism, which I'm not necessarily wedded to. I think there is a conscious agent who makes (constrained) choices. But I also think the Buddhists have a point that the agent I call "myself" is not some stable, eternal thing. It is constantly changing, molding, and being molded in concert with the world around it.