That last part doesn’t sound right but I wish it did.

every interaction that additional user makes with tweets viewed by those 100k existing users requires 100k updates pushed to those 100k users’ pages. Every like sends an update of +1 like on the tweet to every one of the 100k users. It becomes significantly more expensive per user engagement.

This is not how a reasonable API works and is probably not how Twitter “pages” work. A “+1” just changes a number in a database from, say, 629644 to 629645. The latter is no more expensive to send over the wire to a client when it requests data.