An altcoin being on the "top" doesn't automatically mean it's a "safe" or good investment. I mean, take a look at it! The cryptocurrency market is full of crap. And not to mention that bitcoin is risky and volatile enough for the typical inexperienced investor, and you're going to say that it's better for them to buy coins like Ripplecoin a.k.a. fidget spinner coin? Worst investing advice I've read yet.
Supported... Just because an alcoin is at the top list on coinmarketcap doesn't mean investors are safe to invest in the project. I can't advice anyone to go all in on ripple coin cause I myself don't see that project to have potentials, they are better projects out there like $NEAR, $HAPI, $PYR and more you just need to DYOR before investing. Not a financial advice though