An index fund would be yet more diversified, and that's one trade. Very few individual investors have any reason to believe they can pick stocks in a way that outperforms the market.

The zero fees might still be nice if you want e.g. to contribute every paycheck; but an old-fashioned Vanguard mutual fund would be just as good for that, or many brokerages have zero fees for specific classes of ETF. The only advantages that I'd see to Robinhood are (a) no minimums, and (b) pretty UX.