>I feel that by having my investments in Robinhood, I'm adding some sort of risk multiplier that has nothing to do with the nature of my investments. It has to do mainly with how amateur-ish their brokerage operation feels.

In the sense that they'll collapse and you'll lose your portfolio, or that they'll be down at a critical time you want to make a trade? For a buy and hold type of investor, the latter isn't really a concern.