Gmail is an email service. Like the fediverse, email is federated.
By changing your email provider, do you really lose anything? You can still contact your friends, contacts and even various customer suports. You also can recieve emails from popular social media apps. If you degoogle from atleast one Google app, maybe Gmail could be the easiest and least life changing one.
While, Youtube could easilly be one of the most difficult to degoogle from. Not like literally but emotionally. Like deep down you know you can find mostly all you might need on something like Peertube but not all the entertainment media like on Youtube. You will also become a social outcast if peertube is the only app you use. You might not understand channels people mention in day to day talk from youtube or references.
If you use exclusively fediverse apps and sites, Chrome could be almost just as easy to replace as gmail, longterm. However If you use Youtube it won’t surprise me that Youtube downgrades your performance and user experience in what ever means neccesary on competing browsers.
To people hesitating, the path is simple and safe:
Create your new email (I’d recommend your own domain but you can also use another provider)
Set up Gmail so that it redirects all mail into your new mailbox.
Start giving your new email and migrate little by little your accounts to the new email.
You will not lose emails sent to your Gmail but you won’t use their UI anymore.
At some point, you will realize nothing but spam ends up on your Gmail and you can close it if you want.