For me, the purpose of logging in to my Mozilla account in Firefox is to sync saved passwords and tabs between devices. If I was a Chrome user, I would want to log in to Chrome for the same reason.

The problem for me is the fusing of the browser with a preferred 'platform' of services. I don't want a partisan browser.

Chrome is a browser, not your Google account?

The purpose of logging into a browser has always been to synchronize bookmarks, settings, and extensions.