Buffet is no great stock picker, & i don't think he nor Munger has ever claimed to be, certainly not since they stopped with cigar butts.

Buffets great success is due to 3 reasons:

1 Insurance float. insurance premiums are invested in business that throw off cash. this, when payouts are required he has a diversified portfolio plus cash flow to meet obligations.

2 - allocation of capital. Sees Candy needs cash? take some from Burlington Northern. Geico needs cash, Precision Castparts has a surplus., etc etc. Buffett himself has said tha5 allocating resources amongst his companies is his greatest strength.

3 - his name gives him great deals when distressed companies need an investment. look at the GS preferreds he bought during the GFC

none of these has anything to due with the marketable securities he buys , & those stock investments are a very minor part of the company