Checking for extensions is barely anything when you consider the amount of system data a browser exposes in various APIs, and you can identify someone just by checking what's supported by their hardware, their screen res, what quirks the rendering pipeline has, etc. It's borderline trivial and impossible to avoid if you want a working browser, and if you don't the likes of Anubis will block you from every site cause they'll think you're a VM running scraper bot.