Sure, customer reps shouldn't help with account recovery unless they get proper verification. I'm sure many companies have learned from past mistakes. I think that's the only way to solve it. I'm not sure though if this is what has happened here... These crypto people seem to have hacked many accounts last year.

Maybe related video from Linus Tech Tips incident last march: https://piped.video/watch?v=yGXaAWbzl5A

Adam Koralik talks a bit fast and some details aren't clear to me. For example if he got recovery mails and sms from his own actions or if this was the scammer. Also I'm not sure how 2fa works with YouTube. I certainly hope changing the account password makes it ask for the second factor or it's next to useless. If this is the case he must have gotten phished or there is another unknown security issue in the process. Or his password didn't get changed in the first place. But that also can't be it since he clearly tells he got the notification mails for a password change and changed recovery methods.

Concerning your edit: I've read that, too. That your connection drops, once a new SIM card gets activated. That might take a while, though, or not happen with some carriers or under certain circumstances. As far as i know a cell network is a crazy mix of technology. And from his description it's not even clear to me when he talks about SMS and when he talks about notification emails or push notifications.

And in other youtubers' videos I've heard they usually seperate their accounts so that it's not the same account for private stuff on their phone and the important youtube stuff all mixed in the same account.