Warren Buffett's Principle: Is the company simple and easy to understand: Is Berkshire such a company?

I recently read Robert G. Hagstrom’s The Warren Buffett Way.
The author digested some of Buffett’s principles, the top one (translated from German) would be

Is the company simple and easy to understand?

I started to read some Annual Reports from Berkshire and while Buffett builds up confidence for his and his team’s management (which would be one of the next principles in the book above) I actually was surprised about the complexity of the Berkshire subsidiaries.
Various insurances, various locations, various industries, housing, manufacturer, leasing, infrastructure and many many more are part of what constitutes Berkshire (oh and I forgot the investment part 🙂 )

So the question actually came up: Would Buffett actually theoretically buy stock of his own company? (Beside the fact that he already owns most of it anyway :D)

While Berkshire appears to be very diverse, as far as I understood the book, diversity is not a special property Buffett actually looks at. Diversity reduces risk but also requires deeper knowledge about the facets of the doings of a company, making extrapolating growth more complex?

Buffett provides a nice way of communicating numbers via his "see-through earnings" but this is only the "numbers" part of what is described as his way of investment. I thereby wonder whether from a "focus investment" point of view Berkshire is actually simple and easy to understand?