Long time no see ~ 
I don't know what's your whole Environment,
but i'm sure that RPI4 Board has enough performence for video streaming.
And! about 6 month ago, i had some project using webcam.
if you are just testing streaming, with "VNC", it might be Wi-Fi network issue or just VNC has low FPS.
give me an hour. ill check.
If you want Faster Storage, use USB booting with USB 3.0 supported.
(Micro SD Card Slot has limited speed) and you can use sata to usb adaptor.
like this.
