Absolutely yes.

That revenue would still go to those airlines. It just would come from the passengers directly instead of the banks. A person who uses miles to buy a ticket don't just do it because they are bored. They do it to solve a problem. Without the cards they'd just pay. Every day thousands of people decide whether to use miles or pay cash to fly or upgrade. Without the miles, they just pay. The credit card miles are nothing more than a loyalty program that ties them to a specific airline.

It would be like saying that the big 3 don't make any money on economy seats, that its breakeven and all the profit comes from first class. Or that if you only count window and aisle seats the airlines are breakeven, but the middle seat revenue is the profit. You can't just parse the revenue that way because its all baked into the same bag of income and expenses, just like credit card "revenue". Also there is a cost to carry those passengers who use miles, so its not "all profit".

Bottom line is that its not relevant because almost every airline has some credit card deal, but all airlines do not offer the same route network choices. If you want to fly from Boston to Tokyo, you really only have 3 choices of US airlines, regardless of what airline credit card you happen to have.