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.
I just get why you would need such an advance interface for a simple emailing service where you just send and respond to emails. If the emails send, shouldn’t the be enough? It’s not like you need a crazy search API like Google’s to even come close to comparison with them. The email experience really isn’t impacted that badly. unless i’m missing something here.