"strength in numbers". ≠ "economies of scale"

The former is about relative group size, mutual defense within the group, and reducing the risks of aggression against outgroups.

The latter is about increasing the effectiveness of coordinated activity more generally (which, yes, can include defense and aggression), especially those activities that persuade people. Winning hearts and changing minds about issues, especially across faction/party lines.

Making common cause with others who mostly share your views, even if the issues you most care about aren't the same ones, is just good tactics. Making common cause with those you mostly DISAGREE with on the issues that you DO agree on is good STRATEGY.