Okay, so would I be correct to assume that you claim it is in the long run impossible to beat the market except by dumb luck?
I don't see how this follows from your reasoning. You've allowed the possibility of beating the market if an individual trader has some knowledge or insight which the average of the rest of the market does not. So presumably an investor which only acts when he has such knowledge would beat the market also in the long run.
The EMH grew out of the empirical observation that prices wiggle around randomly (and the different forms look at different ways available information could be responsible for that).
Buffet himself, in the letter, has already said that most investors start with comparable amounts of information and capability. So speculating by buying and selling according to predictions of future values of stocks will eventually cause a regression to the mean.
Buffet disagrees with the EMH but he agrees with the conclusion that you can't beat the market by speculating on the movement of prices. He basically lets the random wiggle happen, and when a price dips to what he thinks is a bargain, he buys.
The problem is that we struggle to test the null hypothesis. We can't create 1,000 parallel 20th centuries with 1,000 Warren Buffets to see if he comes out significantly ahead a statistically meaningful number of times. We can only compare him to chance. In a sufficiently large sample, long streaks of perfect performance can emerge purely by chance.
So what you're saying is that it may (or may not) be possible for an individual inevstor to consistently beat the market through skill, but that it is impossible to verify whether an investor who beat the market is in fact skilled or just lucky.
If you believe Buffett's thesis that skilled value investors who do their homework consistently beat the market, it stands to reason that there should also be other strategies that consistently beat the market (let's say over 20 years or so). It also stands to reason that value investing, since it is such a heavily publicized strategy, probably does not beat the market today, since it is such a widely published and acknowledged strategy.
I don't see how this follows from your reasoning. You've allowed the possibility of beating the market if an individual trader has some knowledge or insight which the average of the rest of the market does not. So presumably an investor which only acts when he has such knowledge would beat the market also in the long run.