Yup, I'm coming to a very similar realization. 

Putting common interests first leads to group chats / communities as a natural solution. Instead of filtering out those interest from a public feed that has every fart anyone makes about anything. 

But: 
1. Often you want to share a thought or question with more than one community since interests and topics tend to overlap. This is the huuuuge opportunity current solutions miss and something Nostr is architecturally built for. 
2. Big Tech communities don't have free market forces driving the conditions and costs for accessing those communities. So they can't allow this.