Don't keep your hopes too high.
I am slightly more hopeful than i would have been in your LY situation.
1. This was a paid revenue ticket. (While to me it makes no difference, to others, they may question the entire transaction.. was ot bartered or sold? Etc..) This ticlet was a squeeky clean revenue ticket.
2. Unlike in your case, we were given a reason verbally and in writing that:
"United Airlines rebooked and ticketed you incorrectly in First Class on Lufthansa. Your original ticket with United Airlines was for Business Class and they should have only rebooked you in Business Class on the alternate routing with Lufthansa. The Lufthansa colleague in Miami was correct in denying the rebooking as it was not valid".
This was their response at Miami and with the DOT - and LH copied the DOT on this response originally.
It is not the issue of being bumped that i have brought up at all, but the issue of an airline, using partners to expand their sales distribution - but then using unfair business practices to disadvantage consumers who book through their expanded distribution - by claiming those partners sales as invalid and then placing the onus on the customer.
A fair business practice would be to place the onus on the seller, as customers must be able to purchase exchange and trust their tickets and re-accomodations will be honored...
In the eyes of a regulatory agency this practice has already been ruled on.
Deceptive practices with air tickets are federaly prohibited. This includes charging a fare difference on a issued or exchanged ticket. Simple as that.
Will see what they say...