I hear this a lot but it seems like first ordered thinking. Final settlement assets are not actually used in this fashion historically.

The primary layer is to settle quarterly and yearly major expenses. The way it is used today can't continue for the length of its adoption but the coupon currency layer solves this problem very easily.

Having your own UTXO is the equivalent of your entire stockpile of gold, let's say. In a single day, with not the flat "population of earth" but the economic actors of earth, the block space of an entire day would likely be very empty after the proliferation of Layer 2 tech.

I don't mean to bombard you with economic distillations of layered money but if I were a coder and not an absolute economic goblin, I would focus my energy in creating a robust Layer 2 coupon that was nearly as verifiable as the underlying asset itself. The normal economic actors (banks, likely once regulators stop holding them hostage) would act as lightning node runners or mints (in a more custodial world) becoming a bridge between vendors and customers using existing financial relationships. This is almost inevitable. Only if, the tech is robust enough for the Visa level throughput of 65,000 transactions per second. THAT is where Bitcoin succeeds or fails.