lightning is a pain to set up, you have to open a channel and keep funding it - so if we are talking about small amounts these costs should definitely be added to your calculation. or you use lightning via an exchange - but that again kinda defeats the purpose of bitcoin. in fact all of this could probably be achieved much simpler by just using a stablecoin on tron, solana or one of the ether chains and forget about the whole lightning sending and bitcoin hedging. I doubt you can get lower transaction costs end-to-end staying on btc.

I would guess the price for payment processing drops tremendously when you don't need to handle fraud or chargebacks at all. It's for sure worse for consumers but I do think it has its place (for example adult content that has huge chargeback risk or straight up blocked by other processors).

Monero is even cheaper and more useful as cadh because it's private. Anyone can see Bitcoin history and where the user got their coins.