It's funny you mention this, because I've heard from people who've interviewed with Robinhood that they're still on a single monolothic RDS instance for a good

It's funny you mention this, because I've heard from people who've interviewed with Robinhood that they're still on a single monolothic RDS instance for a good portion of their main application. If I had to guess, a single RDS instance would be a more likely cause, something like a table growing too large (an audit log table perhaps).