since YouTube updates the ranking algorithm every few months, better conduct fresh test to get the best answer for your question.
all i can tell that from my past tests (few years ago) - back-links didn't change much in rankings, i made many tests with GSA .
and on google search, i think they just take the #1 video they have on (google video search) and add it to the google serp and that's usually the #1 video on YouTube for that term.