There are many of Nolan's movies that I love and I have no problem whatsoever with understanding the dialogue. I use my 2.1 DIY system. In my room I get full range sound with great sound stage and imaging and even though everything is only stereo and phantom, I can say that audio is at least carefully mixed. Speech is never masked by any of the ambient noises or loud low frequency effects. When someone is coming in to the scene saying something, his/her voice is nicely panned.
More recently, I watched Dunkirk again. To me, not only speech but everything else about the sound is clear and I really can't fault it. And I tried quiet, as well as "reference" levels. On the other hand, I understand that ambient noises of the movie are such that could easily mask the dialogue and that Tom Hardy is literally wearing one, no pun intended. In recent real life situations I think most of us have, at least once, had hard time understanding people wearing masks. In the movie, I think this is just for the sake of realism.
Anyway, my system is one of a kind so I really don't know what is going on in multichannel reproduction that people are complaining about. But I suspect that it's about the quality and/or setup of the center channel speaker, above all. Possibly it's integration with left and right mains, calibration, room acoustics?
And in theaters, is there even a remote possibility that people bet blasted with so much SPL that they can't even understand each other when they get home?
"According to Sir Kenneth Branagh, roughly thirty Dunkirk survivors, who were in their mid-90s, attended the premiere in London, England. When asked about the movie, they felt that it accurately captured the event, but that the soundtrack was louder than the actual bombardment, a comment that greatly amused writer, producer, and director Christopher Nolan."
Please don't get me wrong, I believe you all saying about this Nolan thing, It's just me having no problem with it. To me, his movies are well worth watching. Dunkirk is a movie about war that never gets ugly. In Tarantino's movies, dialogue is pristine and the greatest, before things inevitably get ugly.