Bigger blocks would - for one - make these kinds of attacks more expensive. This stress test is only slightly effecting others because OP is burning coins as fees and miners are - as its intended - greedy. If the max blocksize is 2 MB the same attack would have needed 40 BTC instead of 20 BTC[1] to have the same effect.
Why do you assume the price of a transaction the txfee will stay the same as the supply of transaction space increases? This contradicts
the law of supply and demand. The price should go down when the supply increases and normal demand stays the same, and the cost of the attack against 2 MB blocks will be exactly the same as the cost of an attack against 1 MB blocks.