Why does it not seem likely that spammers would attack YouTube and try to use their redirector to attack users to you?
The pattern attackers would use is to figure out how to use the redirector at
hxxps://www.youtube.com/redirect?event=channel_description&redir_token=QUFFLUhqbGhxcFJubU9YV0RqWkY3bVlnQUdtZFBTSG5Dd3xBQ3Jtc0treWdqWS1ZX2tFdWlUa3NmY09tc2RUOFN6VUh5WDB2eTFGbE5hUTlFY25VZHROLVgyMVRJR2Mzd0QySUxidGNHYkNOd1FqQXNsTk1zcFBLWF83UHMxTDRIaGdsSGJfRjFveHlwNS1FbUt6bXg3TmhFRQ&q=http%3A%2F%2Fwww.penguinrandomhouse.com
to point at www.looks-like-youtube-but-is-phishing.ru instead of ww.penguinrandomhouse.com. Then, when the attacker manages to take over someone's Facebook Messenger account, they send "check out this cool youtube video" to all of that user's friends. Because the URL has the domain youtube.com, it's trusted, so the'll click on the link. If the redirector simply redirected, a non-zero amount of victims would then have a tab opened to www.looks-like-youtube-but-is-phishing.ru that says they've been logged out of youtube, enter your username and password to login and watch this really really funny cat video that your mom/boyfriend/sister/crush/whatever just sent you.
This kind of interstitial warning was very common on old web forums to prevent people from being tricked by third parties with malicious links. I understand why you'd worry that Google might have reinvented it for self-interested purposes, but if that were the case why wouldn't they do it all the time?
The pattern attackers would use is to figure out how to use the redirector at hxxps://www.youtube.com/redirect?event=channel_description&redir_token=QUFFLUhqbGhxcFJubU9YV0RqWkY3bVlnQUdtZFBTSG5Dd3xBQ3Jtc0treWdqWS1ZX2tFdWlUa3NmY09tc2RUOFN6VUh5WDB2eTFGbE5hUTlFY25VZHROLVgyMVRJR2Mzd0QySUxidGNHYkNOd1FqQXNsTk1zcFBLWF83UHMxTDRIaGdsSGJfRjFveHlwNS1FbUt6bXg3TmhFRQ&q=http%3A%2F%2Fwww.penguinrandomhouse.com
to point at www.looks-like-youtube-but-is-phishing.ru instead of ww.penguinrandomhouse.com. Then, when the attacker manages to take over someone's Facebook Messenger account, they send "check out this cool youtube video" to all of that user's friends. Because the URL has the domain youtube.com, it's trusted, so the'll click on the link. If the redirector simply redirected, a non-zero amount of victims would then have a tab opened to www.looks-like-youtube-but-is-phishing.ru that says they've been logged out of youtube, enter your username and password to login and watch this really really funny cat video that your mom/boyfriend/sister/crush/whatever just sent you.