Paper cash was an innovation to solve the issue that gold is hard to lug around. And very much an analogy of a L2 network

It is arguably easier to counterfeit than gold (there is fools gold too…)

The base layer is very secure. L2s will be faster, but have a trade off of being less secure.

Note: the L2 Lightning Network is different than L2s for ETH like POLY, POLY has its own market cap (garbage idea IMO). Lightning is just a tool to make BTC more efficient