I took the CMA exams back in 2017 before tackling the CPA exams in 2019/2020. The four exams vs two definitely makes the CPA exams feel like a marathon, but I think the content of the CMA exams can be very difficult for many because typical accounting curriculum in most US universities do not emphasis cost accounting the way they do GAAP and standard financial accounting. For this reason I found the material to be more challenging, as I was not that familiar with many of the topics, such as flexible budgets and transfer pricing. The benefit of this (and why I would HIGHLY recommend the CMA exam to any motivated accounting/finance professional working in industry or consulting roles) is that by studying for the CMA you learn highly applicable concepts and skills that many traditional accountants do not possess. In my opinion, to say BEC is a slightly slimmed down version of the CMA exam is an understatement as the depth of the testing is far greater on the CMA exam.
All that being said, the CPA is not to be taken lightly. FAR tests on a wide range of topics that even those working in public accounting are likely to not have encountered. Tax is a technical field that does not always follow the logic that GAAP follows which makes REG challenging. Auditing is fairly conceptually, but without real life experience to apply these concepts to, I can see how the exam would be extremely challenging. I am confident that if I did work in tax and auditing while studying for REG and AUD, I would not have done as well as I ended up doing no matter how much more I studied. For this reason I don't necessarily agree with studying for these tests before gaining hands on experience, but different things work for different people.
Another item to keep in mind when looking at pass/fail rates is that many more people who take the CMA than CPA exam do not have English as their first language. We all know how are difficult these tests are. Now imagine trying to decipher the multiple choice questions in a language that is not your first…I can't even speak a second language, yet alone take an exam in one, so I suspect language alone drags down the pass/fail rate for the CMA being as the CPA is taken by mostly US based applicants.
Anyways this has become a long post, but in summary: I would not underestimate the CMA exam as it tests concepts that your average CPA applicant is likely to not have much exposure to. I went to work in private industry out of school and then switched to public accounting after 7 years to get licensed after having the CMA. After working hard to pass both exams, I respect those who pursue either one or both credentials!