Potentially unpopular idea:
Maybe YouTube search is so bad because videos are poorly optimized for search.
Today most of the emphasis to creators on YouTube is to create content that targets browse traffic and shorts to go viral and get millions of views.
Not so much videos targeting specific user intent with a term that might get 2k views per month if it ranks #1.
Your idea doesn't explain why:
- YouTube search often doesn't return the correct video when we search an exact title
- YouTube search shows entirely unrelated videos after the first 4-5 results