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.
Gmail’s easiest to replace if you have your own domain. I moved mine a couple years ago with no issues at all.
There are still various ways to watch YT ad-free and tracking-free. (And you can pay the creators directly on Patreon or through another service, and watch the videos ad-free on Patron. I pay a little more on Patreon than I was paying for YT Premium, but not much more, and I’m happier the creators are getting bigger cut and Google is getting no cut.)
I use FF basically exclusively except for the rare time a site doesn’t work with it. It was also an easy change. Google does degrade their stuff (whether or purpose or through ineptitude) but there are other options for the other main Google services, as well.
The only things I have left on there are photos, contacts, and calendars. Photos will probably be the next to go.