You can tell how Gunicorn is old by looking at example showing only 4 workers :)
I've seen folks run a $90,000 / month business through their SAAS app using gunicorn on a 2 CPU core box (4 workers).
Nothing wrong with being efficient!
Edit: somewhat typical issue with scaling python applications is that just throwing additional workers at the problem in the same instance of the wsgi container (including separate uwsgi processes) stops being effective fairly soon and makes the problem worse.
Otherwise the number of workers might limit the total throughput quite severely.