In way you are right and in a way you are wrong. Their economists do assume all the costs of taxes are born by the consumer. But they also assume that the costs of payroll taxes are born by the employee also. And then they also assume those same taxes are also born by the employer. It is that type of double and triple counting their benefit that their bought and paid for economists come up with the outrageous numbers they do.I stand corrected.
They even say as much if you read all their propaganda. A tax system that takes out the same amount of money can't by itself do everything they claim. You can't get lower prices, higher take home pay, lower costs just by changing where things are taxed. You can get a minor benefit from compliance costs, but the enormous benefits they claim are obtain by double and triple counting the benefits.