That is absolutely true for newbies. They have too little experience to choose to invest in new projects. However, choosing the top altcoins is less risky but means that they will make less profit. Profits always come with risks, so I always advise them to stay here long enough to make a profitable investment.
I do not think that the old projects that are now in the top will all be promising. I do not see the development of many projects and maybe they simply will die after some time. no matter how big their capitalization is.
After a period of operation, old projects will soon lose the community, and that will make investors tend to leave earlier. I think this is the general situation that any project is facing, so don't hold on for too long if you are not patient enough when choosing to invest. However, you can choose to invest safely by choosing only the coins in the top 20 because these are coins with good liquidity and always attract many new investors.