Thrifty,
I think when you use ROE, people get to valuation represented by a multiple of the book value. The higher roe the higher multiple.
If you mix roe and DCF model, you need to make sure you separate the FCF from earning to do DCF. So in your spreadsheet, you use ROE to get the earnings, you then deduct capex (and dividends), and then DCF on the FCF/retained earning.
Actually I think a better way for valuations is do comparables.
For BRKb, we can compare BRK against UNP, XLU, progressive and then just take the market value of the portfolio. I believe if we take brk’s revenue segmentation weighted YTD market price returns of the peer companies of BRK’s biggest component’s, we will find BRK is lagging by at least 20% YTD.