I think the risk of a quick onboarding via a custodian is that the buyer doesn't understand BTC.
A fool and his money are soon parted.
So they are more likely to be easy prey for shitcoins advertised/offered on the exchange and elsewhere....and likely will get rekt, lose a bunch of $ that could have been invested in sound money.
When someone invests time to studying BTC, they will understand the reason why self custody is important.....they are then likely to stay clear of exchanges, avoid shitcoins and develop diamond hands.
They will also understand it's importance beyond store of value....
🙏