A programming language is like currency. No currency is best, no currency is worst. Some currency is more popular than the others, more often than not, it’s because of convenience.
Is JavaScript the best? Don’t think so. But for frontend, we don’t have a choice.⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
Is PHP the best? Doubt so too. Elixir, Golang, or even Python seems better. But hey, Google and Facebook are using that, so I am not going to argue.⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
Replacing JavaScript in browsers or replacing PHP in the backend is like using RMB to replace USD. How to convince all central banks to hold Yuan as their reserve?⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
Most of the international contracts are priced in USD. International trades are using USD. Before Yuan finally become the global currency, you have Euro, Yen, and GBP lining up in front of you.⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
Before (Node)JS finally took over PHP and become the most popular backend language, you have Ruby, Python, C#, and even Java lining up in front of you.
If you have decided to use a JavaScript stack e.g. MEAN, MERN stack, or even JAM Stack, JavaScript is an intuitive choice. You will only need one language for front-end, back-end, and even database.
If you think you can develop faster with PHP, it could be because of your familiarity.⠀If you have spent the same amount of time coding in ExpressJS you might get the same output, or who knows, even faster?