if your threat model is a global passive adversary they clearly know where payments begin and end.

his (unexpressed) point is "the second and second-to-last nodes on a route can't be sure they are second and 2nd to last"

but it totally depends on the level of collusion between large nodes. a global passive adversary isn't required, if enough large nodes (particularly in a hub-and-spoke design) collude they can have *reasonable certainty* where payments originate and end up.

Add mapping via channel probing and consider.

not saying it happening now,

but I AM saying,if it was happening you wouldn't know.

which is why we have L1 systems designed to function in the open.

That is the advantage of using a blockchain and not an L2.

everything is tradeoffs.