I support skepticism about things like this, but I will say: Wim is not scamming people. He's showing them how to do something that works to lengthen his breath retention underwater and the regulation of his body heat. What he does is similar to pranayama, and dissimilar to hyperventilating in that he's pausing between the inhale and the exhale, a lot like the Navy SEALS.
Wim is not a great public speaker, and English is a second language to him, so what you see as evasion appears to me as a non-scientist trying to explain his experience in a language he hasn't mastered.
If you are going to claim that people have drowned by following his methods, you should link to it. Wim and his website are careful to say that this breathing technique should only be done in a safe place, sitting down. And if people go into ice water they should be supervised.
There is some scientific support, published in the Proceedings for the National Academy of Sciences (PNAS) for a breathing technique that can affect our autoimmune responses.
http://www.icemanwimhof.com/files/pnas.pdf
Briefly, sustained deep breathing mimics and breath retention stimulates the production of epinephrin/adrenalin and influences the autonomic nervous system.
When he came to the Bay, Andrew Huberman brought him into his neurobiology lab at Stanford to run some tests on him. Wim is doing something that deserves attention, and his breathing exercises can help change your mental and physical state. You don't take his word for, or mine. Just try it.