One of the mantras I hear repeatedly in this community is "not your keys not your coins", outlining the importance of self custody. In this regard, is it actually realistic for majority of people to self custody their bitcoin on a blockchain that only supports ~ 7 * 60 * 60 * 24 * 365 ~= 221M tx/year? Doesn't this mean if 1B people wanted to hold their own funds it would require at least 4 years? - this is not even including other miscellaneous transactions.
Lightning seems like a promising layered solution, and I very much agree with this design. But, my understanding is that one of the fail safes to bad actors on the lightning network requires you to open and close channels each consuming a transaction on the main blockchain. While transactions within the lightning network are designed to be infinitely scalable, it doesn't seem to be the case when you need to regularly write to main blockchain. Is it feasible/secure for someone to custody bitcoin only on the lightning network?
Given these parameters, how realistic do you think it is for bitcoin to really become a global money? Did I make any incorrect assumptions? Please enlighten.