Both are acting with monopolistic power in numerous areas and both should be scrutinized. Just because one argument against monopoly power is that incumbents can sometimes rest on their laurels and fail to innovate doesn't make this the sole reason to pursue antitrust action.

Not on you though, this kind of reasoning failure is so common I think it deserves a fancy "cognitive bias" name. Off the cuff maybe something like "Single Rebuttal Fallacy"?