...Let's face it: Bitcoin can't scale on-chain, but LN can't be used to create many channels on-chain either. So for mass adoption, LN has to be largely custodial.
why do you say that?
Because it's not even possible to have just a million people make one daily on-chain Bitcoin transaction each.
For a while I was opening a channel every week or so. Yes I use my own HW & node so it's a bit different.
For mass adoption, I'm thinking about at least hundreds of millions of users who each make daily LN-transactions. That's possible, but not if they all have to open their own channel first.