If he only managed his own funds, his investment universe would be bigger. Why did he not choose to do that? I assume Bill Ackman charges 2+20 in Pershing Square. Wouldn't Buffett be considerably richer if he had done the same instead of letting co-investors in Berkshire come along for the ride for free?
You are forgetting Mr Buffett's is a DEAL MAKER, he would not have produced his current achievements without compromise and concessions in the purchase of businesses. Those co-investors were prior owners of the businesses he purchased.
he has lamented that he would be theoretically richer if he ran a fund. He did have a fund at one point but shut it down. the advantage of having his platform is that no one can redeem their capital. If they want to do that, they have to sell the stock at the prevailing value and he still has the capital.