There's premature optimisation, where you write a whole bunch of complicated code to avoid cloning an Arc<>. And then there's "premature optimisation" where you skip any consideration for performance until it becomes a problem.

The latter is usually what people who use the quote "premature optimisation is the root of all evil" think it means. Don't just keep calm and clone, consider what you're cloning and why, and then hopefully we won't end up with even more horribly slow software.