Replying to myself to highlight one of Justic Thomas' best lines:

"It changes nothing that these platforms are not the sole means for distributing speech or information. A person always could choose to avoid the toll bridge or train and instead swim the Charles River or hike the Oregon Trail. But in assessing whether a company exercises substantial market power, what matters is whether the alternatives are comparable. For many of today’s digital platforms, nothing is."

Beautiful, elegant and intelligently put.