That's an interesting argument because basically any modern Berkshire letter you read is going to say something along the lines of insurance being "the most important" part of BRK, an "all-important" component of their revenue, "the cornerstone of Berkshire", "our core business and the propellant of our growth since we purchased National Indemnity", "our main business", "a huge winner", "exceeds its book value by more than any other Berkshire business", &c.

(Can you tell I just plugged a bunch of random years plus "Berkshire letter" into Google? I didn't find a single one that didn't play up insurance; I'm not leaving any out.)

In 1994, he even laments exiting a position in GEICO in the 1950s as one of his major mistakes!