The "gurus" are talking about managed mutual funds, which is where a "Rain Man" genius stock picker tries to pick the best stocks. 10 years separates the skilled from the lucky. They want you to compare managed funds to each other. Actually, compare them to the index. Make sure to subtract out their expense ratios and loads.
Or better still, compare them to index funds that work in the same domain of stocks, such as VFINX for large-caps. Index funds do in fact have expense ratios, but they should be very, very small (less than 0.1%). So make sure to compare them net of loads and expense ratios!*
In the case of Vanguard, their life-cycle target funds are index funds, those are basically Vanguard's whole thesis (read John Bogle's book). So comparing them to the index is a lost cause, they are the index.
The deal is that the stock market gives the highest growth but high volatility also. If your planning horizon is long enough (>20 years), the volatility averages out and the stock market is such a sure investment that university endowments are in it.
However, as you get near retirement age, you risk getting nailed by a downturn, without enough time left to recover value. So as you get closer to retirement age, you should be migrating out of stocks and into stable but lower growth investments like bonds. Life-cycle funds do this automatically.
So if you want to compare a life cycle fund, you need to break it into its components and figure out what fraction is in bonds, comparethat to a bond index, which fraction is in large caps, compare that to the S&P 500, etc. etc.
Now, the life cycle fund does the blending based on a rigid formula, a clever person could look at market conditions and make big shifts when the market seems to be at a peak. However, that is called "timing the market", and brokers absolutely will never tell you to do that, for a lot of reasons, largely business ones.
* and compare good index funds, like Vanguard's. Every broker which pushes managed funds also has an index fund on their books, rigged with the same 5.25% load and 1.5% expense ratio that they charge managed funds. It's only there to look bad.