Note related discussion in Common rate limiting for all consumers
You are indeed correct that if you have fast-growing usage of your backend service, and you don’t have plans to scale your backend in response, you will have problems - but I suggest that the correct way to solve those problems is by scaling your backend service and/or implementing per-consumer (or per-IP) rate limits.
Global rate limiting has the potential to cause increased usage of your service, by a single consumer, to effectively deny all users access to your service - I doubt that is what you want.