Does your argument still apply if you change "coins" to "cash" and "brokers" to "banks"?

I leave my fiat money in banks because I judge that the risk of the bank disappearing and taking my money with it is lower than the risk of my house getting burgled, catching fire, etc. Likewise, it's entirely reasonable to think that a competent Bitcoin broker is more secure and safe than my half-assed attempt to keep my own keys and risk losing access to my coins through my own incompetence.