the average Joe
I'm pretty sure the average Joe won't hold custody of their funds, and that's neither good neither bad. It's neutral. Over all, it's good that we have the option to opt-in to self-custody. If some don't value it, I'm definitely not going to convince them be responsible. Nor should I; some are just irresponsible, and trust a third-party more than they trust themselves. Even that way, they can use Lightning hubs and be part of the Lightning Network without holding custody.
There will be wallet software which does all this for you in the background. Just as the average Joe doesn't need to know how to actually create or sign a transaction, or how to use change addresses, or how their private keys are derived, they also don't need to know how to actually open and close a Lightning channel.
Holding keys and signing transactions in the background versus leaving an entire computer running 24/7 to enforce consensus rules and check for cheating attempts is not of the same order of magnitude. I don't bet the average Joe will do the latter. Hell, lots don't even do the former.