Your solution is to ban humans from talking to more than 5 others at once?

It is an interesting solution if nothing else. What about capping the number of users or followers to 100 or 1000 other people? That is closer to how humans interacted for the vast majority of history since the development of language. If you think about it, it's extremely unnatural for single people to have direct communication to millions of people. Information can still spread from social group to social group. I don't endorse the idea, but I would be interested to see how it might work and how information would spread and ideas change.

Forwarding WhatsApp messages is a tiny subset of "talking to people".

The subject of this thread is "how do you lessen the spread of misinformation?" across all of social media, and the parent claims that whatsapp has largely solved this problem. So we're talking about applying these restrictions much more broadly.

you can talk to hundred people at at time. You just can't forward the same message to more than 5 people at the time. What's the problem with that?

They can talk to more than 5 people at once, just not through the WhatsApp platform. I take it you think email spammers are also unjustly treated too.