The leetcode issue is to a large extent caused by, literally, leetcode.com the website. When I first started doing technical interviewing this website didn't exist, so if you developed a question that wasn't too easy or too hard, covered the bases, fitted well into 45 minutes, that you could calibrate the difficulty of on the fly etc - basically a good question - then you could make it last quite a long time.
At some point people started sharing questions and pre-canned solutions online, and many candidates will cheat by looking up answers and copying them from another screen if they can. Also some shady recruiters started leaking questions to candidates ahead of time. That forced interviewers to start constantly inventing new questions.
One of the points I used to make in interview training is that questions are like programs, you have to design them. Some are better than others, they can vary in efficiency etc. Often you can't really know how a new question will work out until you try it a few times. Making a good interview experience for the candidate is hard work and it's easy to screw up, lots of interviewers do and it leads to a lot of bitterness (e.g. questions that are far too hard or specific or don't fit in the available time).
Unfortunately if you're constantly having to invent new questions to keep ahead of the people sharing them and grinding the process, then the quality will inherently get way more variable. By the time you've calibrated the question it's been leaked already. And there are a finite number of programs that it's reasonable to ask someone to write in a short amount of time, so by now these giant databases of interview questions and candidates memorizing the answers at scale makes it harder to get accurate information, which was the only goal in the end. Because indeed the specific tasks themselves don't matter much.
