> For example, if you had an MCP connector to United and found a flight from SFO to DEN for $50, the rest of the seats have to go up in price to compensate and not just by a few cents because the nominal cost of an economy seat is likely $250, not $50.

Your premise is false, as it rests on the logic that there is a zero sum game between passengers. Airlines offer tickets at the level and price they feel like they can sell them in the marketplace. There's not some invisible total allocated to passengers on each flight, where if one person "gets a deal" others pay for it.