The only reason adblockers would be to blame would be because Google wanted to make up for lost revenue, similar to the myth of high end department stores having high prices because they expect their customers to shoplift.
The "Login with Mastodon" button isn't like "Login with Google." It just lets you import things like your name, email, handle, profile picture, and follows to use on your new account. You still need to create a password for your pixelfed login.
The only reason I even have an instagram account is because my apartment did virtual tours with it during COVID. No big deal for me to archive all my non-existent posts :)
If you're gonna get a browser with a brave-like experience, might as well get a Firefox based one like Zen.