The older pattern works and the addition in the query string is purely a source tracking identifier if it only appears for sharing. While some will remove that section when sharing, casual users and minors may not and them using it on reddit, whatsapp or twitter would instantly map their accounts, or worse their devices. Will Youtube keep this information with itself only?
And even if Youtube keeps it to itself, non-state actors could still do a simple search with the key value and see if the same identifier appears used in other social media. Convince me how this can’t be taken advantage of by any random person to search someone?