Very true, but that's exactly how it works now. Most people accept Bitcoin (maybe Bitcoin cash too lol, sometimes ethereum) a lot support lightning too. Some darknets only accept monero (in a drivechain future they might also accept zcash drivechain bitcoin).

Point is the reciever chooses.

I usually prefer merchants that accept lightning for the low fees and privacy, but if they don't accept lightning, I have yo go onchain. Incentives are aligned so that merchants accept payments so long as the amount they might earn on that rail outweighs the costs of supporting it (they can factor swap fees into the price for example).