A lightning transaction received in a custodial wallet is an IOU.

A lightning transaction sent with current technology is an IOU due to the inability to verify all the electronics and software in any network segment with 2 nodes in it (or probably even 1 node).

A volume of lightning transactions sent with similar, but more verifiable technology, would encourage custodial wallets, thus eliminating many real transactions and replacing them with IOUs, thus directly making those ones absolute IOUs, and indirectly making all the others relatively more IOU-like than actual Bitcoin transactions (which are also relatively IOU-like with current technology).

You're pretending lightning can't be "overprinted" like paper gold, when it's very easy to understand how it's possible and you've probably seen it happen firsthand. Cult brain does this to you.