I’m thinking your issue is more related to the Pi your using. The Pi Zero may not be up to the task of giving you those frame rates.
I tried using a Pi Zero W with Motion Eye OS and the video stream stuttered a lot. I had much better results with a 3A+. It was a nice compromise and cost saving from going all out with a 3B or 4B. I’m not using all those ports anyway. I run Motion Eye at 720P and get around 30fps. It fluctuates a bit. That’s over 2.4 GHz WIFI.