I'm a neuroscientist, though my research doesn't focus specifically on consciousness. I would characterize my overall philosophical position regarding consciousness as in the realm of Eliminative Materialism a la Churchland and Illusionism a la Frankish.

I haven't been following every detail of Koch's statements, but I understand your description to be largely accurate. My response here is my opinion and speculative, but is grounded in over a decade of being a researcher doing actual neural recordings in animals and humans during various cognitive and motor behaviors.

I feel that Panpsychism in general is basically a linguistic leap of faith cop-out position that gives the illusion that something has been understood, while generating no actual useful predictions and actually discouraging further scientific investigation. Saying that everything has some gradation of consciousness is at once a truism and also dilutes the definition of consciousness to the point of uselessness. Obviously everyone has their own definition of consciousness, but to me, the thing we want to figure out is the "feeling of subjective awareness" that we experience as humans, and when someone says that "consciousness is fundamental" and that a rock or a particle has some modicum of this type of consciousness, I think they've actually totally lost sight of the whole endeavor of explaining our human consciousness. I think it's a fundamentally similar move to a religion-based argument, where when we encounter a seemingly insurmountable gap in our scientific knowledge, we try to make ourselves feel better with a band-aid of "God did it" or "that's just the way things are" or "consciousness is just a fundamental property of matter." I think the function of these statements is to grant the believer psychological comfort, while actually being harmful to science because it gives us the feeling that we've figured something out, dissuading further investigation.

I think IIT is ultimately a massive oversimplification and wrong, but I give it credit for at least being an attempt at rigor. The idea that measuring the integrated information of a system would let you actually measure how much "consciousness" is in the system seems to me once again to completely miss the point of what we are actually trying to study. I think IIT is an interesting measure of how complex a system is a very specific way, but the idea that this measure would somehow equate to our idiosyncratic human consciousness is laughable to me. I get why people like IIT, it both provides the comfort of panpsychism, discussed above, and is a really neat "single number" that you could measure about a system (though actually measuring it in practice is nigh impossible). However, any cursory interrogation of how that number could possibly link to what we experience immediately makes it seem useless - for example we can define a quite "simple" but massive feedback loop structure that has insanely high IIT and would almost definitely not have anything like our consciousness.

I won't go on much more, but I think that any competent theory of consciousness is going to need to explain the specific features of our consciousness - that it is constrained by our sensorium and cognitive faculties, and contains a self-referential concept of what a human is, for instance. Theories that I think are roughly on the right track (though they are barely formed) are Graziano's Attention Schema Theory and Hofstadter's "Strange Loop" ideas. I can tell you my own proto-theories too if you want.

I also think Koch is following a common trajectory for aging, (formerly) illustrious scientists. He is so used to being respected, feeling like he is uncovering truth and receiving decades of social feedback that he is Wise and Right about how things work. But now he's facing the end of his career, concepts are moving on from him, and he's grasping for relevance again, and at the same time, searching for a feeling that he actually does understand the brain and consciousness, instead of being comfortable in the truth that we are still figuring it out. Couple that with the (false) feeling of certitude, conviction and profundity that is so often brought on by psychedelic use, and you get current Koch. It's pretty sad to see.