The argument that we are historically high trust in small tribes, is not a denouncement of the position that we are in a unique moment in history.

Altruism, as you pointed out, is conditional. If population grows, the new constraints change the conditions that determine societal behaviors.

We need to develop tools to maintain a social contract once we grow past a degree of complexity.

We may be recreating the things we value from the small group stage, however our ability to achieve that in the recent past was an achievement.

It took a lot to get there, and tons of ideas and counter arguments were attempted and their failures learnt from.

Even the past moment had huge flaws.