A request for a static file does not have a large impact on the overall server load. The requests for dynamic content are the heavy ones.
In general, a json request is not a static asset that will be cached by a CDN. It is dynamic content which is generated on the fly. Why are you talking about json files in a CDN context?
static requests != heavier load.
I am sorry but this is really bad advice.
This is an example from a 6-CPU machine (so CPU adds up to 600%) running Discourse without a CDN or S3.
You can see that nginx is only responsible for 6.7% (so that is 1/100 of the capacity). Only a part of that is used for static assets.
If we were to offload the static assets to S3 and/or a CDN it would reduce the overall server load by less than one percent.