You are right that aggregate method is different from Fifth Person. In fact both method can work, the important factor is the price and value. you just need to buy business cheaper than the intrinsic value. both method are describe in this speech given by Warren Buffett.
Choosing which method to use is depend on individual preference. If you use aggregate method you have to invest in more than 100 companies. Personally, i can;t track so many companies, most of the time retail investor have their own day job. Hence, if you have to many companies, how are you going to track them unless you do it full time.
I don;t encourage to use this method on a small capital. For instance, you start off with $10,000 and you invest in 100 stocks which is 1% of your capital each. It work out to be $100/ stock. If you invest in $100 in a stock, your broker commission is usually about $30 so it is not really economical unless your starting capital is $100,000