Sure if you want to be pedantic. However even if you double the number of rounds, the number of operations required to brute force increases by only a factor of

Sure if you want to be pedantic. However even if you double the number of rounds, the number of operations required to brute force increases by only a factor of 2. Since the number of operations is likely to be a very large number already, such a change is insignificant and we can consider the brute force cost to be independent of the number of rounds which is usually a small integer.