I'm saying this because i myself have, and lots i know, have launched production sites with 100s of thousands of users on ready-made stacks like, Laravel, Rails, Flask (Php, Ruby, Python). But it's my impression that these fall short on millions of users and enormous concurrent traffic, but then you're already at huge evaluation, years into your project, or have 200+ positions, ie. you've already refactored your project multiple times.