You wrote.... "you can just rely on such packets to be sent to the sender if the payment cannot go through due to insufficient liquidity" .... Right -- "temporary_channel_failure" -- here

GitHub

bolts/04-onion-routing.md at 2b9c73b48c1920df8e7e867d110fab2d720a059b · lightning/bolts

BOLT: Basis of Lightning Technology (Lightning Network Specifications) - lightning/bolts

. The issue is that hitting failures like this has the effect of increasing payment latency for users, and also, if there are too many failures, the payment will time out entirely. Shouldn't we, for the sake of users, be trying to insulate payers from potential failures? And ....isn't a good way to do THAT is to simply signal to the network "hey, don't use this channel in this direction, I'm signaling this by putting my fees high"..... ?