Not entirely true. Take the recent controversy around YouTuber Markiplier having users' accounts shut down (including both YouTube and Gmail) for spamming his YouTube livestream chatroom.[1]

I also did a quick search and it's been a while since both Gmail/Google accounts and YouTube accounts are tied to one another.[2][3]

[1] https://www.businessinsider.com/markiplier-youtube-fans-heis...

[2] https://webapps.stackexchange.com/questions/1692/how-do-i-un...

[3] https://support.google.com/youtube/answer/69961?hl=en