Yes, Warren is a smart guy. He actually does recommend CSEW40 in his book "HOW TO MAKE YOUR FIRST MILLION"

- suppose you haven't read it
Quote from warren on JustOneLap:
The CSEW40 is a great hybrid between a normal (pure) index tracking ETF and a more active ETF such as a RAFI or DIVI investment that has an element of decision-making that can impact the investment positively or negatively. The most valid criticism of index tracking investments is that one or two shares could become so large in your investment that you effectively have no diversification. If you try to address that issue, you need to do so without trying to predict what investments will do well. The CSEW40 strikes a great balance because you get the same shares as a normal Top40 but each share gets the same allocation. This means the costs of the ETF can be limited and there are no “active” decisions that might harm your performance. I also like the fact that you get a larger than normal allocation to the smallest companies in the Top40.” -
https://justonelap.com/etf-csew40/
STX40 is NOT the same as CSEW40 - Yes, it is the same stocks, but different amounts of exposure and therefore different risk.