It is a strategy for those that are not capable of doing a real investment analysis. If you are unknowledgeable and just want some general market exposure then investing in the top coins by market cap or even better a fund that tracks the top coins may be the best strategy. If however you have some skills and are able to determine what will separate the winners from the losers then investing in the smaller cap coins that are highly undervalued can offer significantly better returns.
I understand what you are suggesting but as a fresher in the market, the volatility is quite unnerving. Maybe with time I would be more confident and understand to analyze better but to at least start the investments, you think its always safe to invest in top ranked?