I know nothing about how WiFi works; for all I know it is carried by Pixies. However my experience on sites of all sorts is very variable. Two factors appear to affect it. One is coverage by the WiFi masts( the thing the pixies fly from)- in some places being at the edge of a site, for example, means the WiFi is rubbish. The second is how many folks are using it. Some places don’t have enough pixies to go around so it is poor when the site is full.
Haven’t been on enough C&CC sites to be specific about those.
Mel