I think the technical "implementation" of one's adoption is secondary to their mindset.

Everyone running a full node is a pipe dream, at least for now, perhaps forever. You can't expect everyone to shell out a couple hundred $ for Raspberry Pi or an old computer + invest the time and effort to maintain their channels etc. to be considered a "proper user" of Bitcoin. Fiat system does not require this, so this expectation would actually be counter to adoption as defined by "number of users".

Regarding self-custody, I think we should acknowledge that custodial wallets are great for onboarding new users. It would therefore be hypocritical to discount users of these services as "adopters".

And custodial solutions are completely acceptable for holding small amounts. It's a risk management excercise of convenience (funds held on a well-connected node) vs NYK-NYC.