He doesn't favor the EITC over increases in the wages of the poor because he has calculated that it will mean more profits for himself. He believes that it is the best way to proceed to improve the lot of the poor because he doesn't understand the economics involved, including the role of the investors like himself.
He would probably agree with Loren and most of the free market enthusiasts here. That the labor market is a fair market where wages are set to the marginal productivity of the labor. That to increase the wages by an artificial means like increasing the minimum wage will distort the labor market, resulting in unemployment.
He is approaching the problem with a faulty set of economic tools. It is worth pointing out for example, that his toolset doesn't have an equivalent concern for profits exceeding the marginal productivity of capital, causing economic distortions in the capital markets. It is reasonable to assume that if marginal productivity plays such a key role in one market it must play an important part in the other.
It actually doesn't play a part in either, the labor market is exactly what it appears to be, one that is not a fair market unless the economy is at full employment and full utilization. Even then the employer has considerable leverage in dealing with his employees.
Disclosure, I own Berkshire stock and have the highest regard for Buffett's abilities as a value investor. I have less regard for his abilities as an economist.
Given how well he does at economics I find a simple assertion that he's wrong without providing any reason to be highly suspect.
And he doesn't have a concern for excess profits because that is self-correcting in time. Trying to fix it is worse than not trying to fix it.