It sounds so ridiculous for anyone to invest just because a coin is on the top list on cmc, that's the worst investment decision imo.
Invest in a project base on quality, standards and team, it can be a new or already existing project but it shouldn't be because of the top 100 list, the position is not permanent.
If they choose the coin without analysis, it is not a good decision because we know that the coin on the top of the list will surely be replaced by another coin that can get more support, and the project has more opportunities to develop. But if he chooses a new project, he has to look for more info because he has no idea what will happen to that new project in the future. Perhaps, we can suggest he buy bitcoins instead of altcoins due to the change in coins at the top of the list.