You make many valid points and I want to address some of them here:
1. My belief of what a qualifying exam is that it’s almost the only time an external expert, someone not the advisor, gets an opportunity to gauge the readiness of the student for a PhD. You are correct that a competent unbiased advisor will already know if the student is ready for a PhD but the two adjectives in this sentence make the case for why independent external evaluation is needed in such a case. I worked with advisors who eventually became antagonistic to my interests and I depended on the quals and viva exams to make sure they don’t screw me over. I also lived through multiple generations of PhD students going through this lab via many universities and grad programs, and every program with lax quals only enabled advisors to have outsized influence on the students future (either for better or worse). So hopefully I have made the case for why external evaluation is necessary.
With that convinced, let’s then ask how best can external evaluators gauge a PhD student? Written work might not work since you can never tell how much help they had. In fact I feel you can never trust anything that is “take home” Because at the graduate level it’s hard to evaluate an individuals’ contribution to a piece of research. Which only becomes harder in the more collaborative environments of today! So I’ll be curious what you think the solution here is if viva exams are not equitable.
2. You are correct that some people don’t do well under the time pressure of things like quals. But unless there’s a viable solution for problem 1 above, i feel this is an acceptable compromise. This is not an exam where it’s determined you get basic rights, it’s an exam to choose elite members of a society that should be meritoriously selective. And as grueling tests go this seems the lightest! Just an hour of grilling by 4 people in closed doors, and you get
Multiple chances and infinite time to prepare! How much simpler can it get?
Further, how sure are we that this skill doesn’t indirectly transfer to their future career? You are correct that phds can be productive without ever talking to another human being but doesn’t mean this skill isn’t important or helpful. This is like asking the navy seals training to become less strenuous because it could exclude people and maybe because carrying logs doesn’t directly apply to their future career! I’d argue it does tangentially help and given the lack of alternative testing methods this seems perfectly acceptable.