If Buffett thought he had a better choice, why wouldn't he have done so?

Because he doesn’t own the world. Even Buffett has a finite set of options and multiple constraints. I’m not saying Greg was a bad choice. He may simply have been the best choice Buffett had, but that by itself doesn’t tell us much about whether he can meet the challenges Berkshire now faces.

I’m getting a bit tired of beating up on Greg.

I don’t think anyone here is interested in beating up Greg or bad mouthing Berkshire. Could it simply be that some of us, without such a strong vested interest in Berkshire’s success, are more willing to challenge the assumptions? A recurring trap in investing is that the more committed we become to a company or thesis, the harder it can be to question its key assumptions without unconsciously defending the conclusion.

In Berkshire’s case, the question is not whether Greg is a good man or a capable operator, or whether Buffett left him a difficult hand. The question is whether the assumptions required for Berkshire to generate meaningful outperformance are actually supported by evidence. Given Berkshire’s size, its enormous capital base, the maturity of many of its businesses, and the change in capital allocator, I think those are entirely reasonable questions to ask.