WhatsApp only allows eight person vid chats.
Much as I dislike Facebook, I think this restriction is based upon the underlying Signal implementation which, as it uses end-to-end encryption, can't use a server to offload multicasting. However, as it's not always clear when WhatsApp uses e2e, I could very easily be wrong.
Otherwise it's nice to see some competition here though I'm sure it's only a matter of time before someone buys Zoom. Microsoft seems to be shadowing Google over the size of group calls. I've always found Hangouts to be rock solid on the phone and a big of a hog on the desktop. Teams, at least for MacOS, seems to be the worst of all worlds, but connections are generally stable.