Nowadays virtually all merchant adoption uses Lightning. And lightning is 100% up to that. Anybody who says otherwise lives in the past. OK, I concede 99+% :)
But the big problem is with incentives. The vast majority of merchants don't have the incentive to accept btc. And nobody can force them.
In the west, that's probably true - and they'd need another reason, like ideology. But it's still happening - eg see lugano - and that just means they are Our People, you can go along and meet your family..
But in other parts of the world modern payments are very problematic and have much greater costs. In this case it is perfectly possible that what seems to be true, is true: lightning is cheaper for them.
