That's just the problem though, isn't it? Because the leetcode format is known, unless the person tells you, how would you know they studied for months to pass it?
Brilliant person A does leetcode for a week to get the hang of the format, then interviews and gets a job offer. Person B who just isn't brilliant but is highly motivated, studies leetcode for months, interviews, and also gets the job.
You might have fantasies of outlawing "studying for months for the test" but be real. Person whos "is just not cut out to be a high level programmer, and should consider a career path more suited to their abilities", it turns out, is doing just fine with their career path having studied for the test.
I also think calendar time is the wrong way to measure it, since there's a huge difference between studied leetcode for 40 hours a week like it's your job or being in school; and studied leetcode for 4 hours on Friday nights instead of going out, for months.