You can do anything you want if you are into managing a huge spaghetti node system.
Sometimes its more efficient and especially flexible to be able to write code, and easier to maintain, update and edit.
Same would happen with code if best practices aren't taken into account.
Blueprints provides the tooling to package stuff into re-usable components, exactly to avoid spaghetti code, just like in most graphical programming languages.
I wouldn't do networking in blueprints. But for your core gameplay ? It can absolutely do anything you want.