"When individuals interact locally, the outcome is a stable plural patchwork of cross-cutting conflicts. By encouraging nonlocal interaction, digital media drive an alignment of conflicts along partisan lines, thus effacing the counterbalancing effects of local heterogeneity. The result is polarization, even if individual interaction leads to convergence. The model thus suggests that digital media polarize through partisan sorting, creating a maelstrom in which more and more identities, beliefs, and cultural preferences become drawn into an all-encompassing societal division."
So the paper is supporting exactly what I'm saying. That in your local community you need to engage with differences of opinion to successfully navigate local social structures, but that online with an expanded network you can interact with only like minded people.
Yes, the overall bubble is larger online than in real life, but as a result it allows for self-selecting subnetworks which align with confirming your biases and further radicalization rather than compromising with differences of opinion.