To the senior engineers who are already happily employed and hate leetcode interviews: An effective way to fight against this is to start saying no to these interviews. Senior engineers have the power to change this if it becomes a trend to say no to these interviews. Anytime a recruiter contacts you on Linkedin, ask them does your interview process include leetcode style whiteboard interviews? If they say yes, then politely decline and make it clear that's the reason for the decline.
All the leverage is on the happily employed senior engineer side. If they're not happy or unemployed, then it's different. But for the happily employed, it's the recruiter/company trying to convince them to leave. And it's very reasonable to reject these interviews. An employed senior engineer already has a demanding job that requires at least 40 hours a week. And since they're older, they're likely to have other responsibilities like family. There's simply no time to grind for months on pointless leetcode problems.
If more senior engineers start immediately rejecting any recruiter messages with a simple "No, I don't do leetcode", the signal will be sent. Recruiters will start getting frustrated and tell hiring managers, hey many of the great engineers I contact keep saying no because of this leetcode thing, can you change that part of the interview? I can't find any good candidates because of this. That will force hiring managers to really evaluate if this leetcode interview is a good idea.
Don't be fooled if they say it's not about getting the problem right or they just want to see how you think about a problem. That was somewhat true a long long time ago when these types of interviews started and leetcode didn't even exist. And it's what they still say to make it seem reasonable. But the reality today is that the interviewer only cares that you can write out the optimal solution within the interview time. That's it, that's all the interviewer will care about. If you don't have the right answer, it's an immediate zero. They might care about other factors (like are you friendly, code quality, etc.) after you successfully write the optimal answer on the board. But writing out the optimal answer is the baseline, they don't care to evaluate any other factor until that baseline is satisfied.
There might be a few interviewers who still try to stick to the old way of these interviews, the original intent. But statistically the odds are against you. These interviewers are generally older and becoming fewer and fewer. The new generation of junior engineers are becoming senior and they only know the leetcode grind. In a typical interview loop, it will become more and more probable that there's more and more of these interviewers who expect the candidates to have done the leetcode grind and base their evaluation from that assumption.