just like Software Engineer having to pass leetcode round and system design round, I also doubt that ML theory and practice is much harder than system design (theory and practice). Beside that, you get paid more than Software Engineer.
I can tell you we are not paid more than Software Engineers, but that might be only my company.
One startup asked me this. They gave me a very vague problem statement, and in 2 days I had to find a couple of recent articles relevant to the problem and prepare a presentation explaining my solution and justifying my decisions.