> why they ask questions to assess your ability on the actual job

You already said LC isn't an ideal proxy to the job. So I am not sure what point you are making.

If I work at Stripe for 5 years as a software engineer, are you saying I am lying about my experience? How about Google? How about Coinbase? How did these people survive for so long?

It seems like you default to the candidate being liers. Maybe you are young, but it will happen to you one day, once you learn the full-stack and then realize no-one cares because you need to pass LC to even get a job. Something you don't need because software engineering encompasses much much more than some DSA algorithm.