Unfortunately this is pretty typical Lufthansa behavior.
If the crew documented it, that’s good, but Lufthansa almost never proactively offers compensation for broken IFE. They’ll apologize and wait to see if you go away.
What most people end up doing is replying back and being very specific about what you’re asking for. Something like a goodwill voucher or miles. Don’t ask if they can compensate, ask what compensation they can offer given the documented issue on a 14 hour flight.
For reference, what people usually get in similar cases:
A few thousand Miles & More miles
A travel voucher (often €50–€150)
Sometimes nothing if you don’t escalate
Broken IFE isn’t covered by EU261, so it’s purely goodwill. That’s why you have to be persistent but polite. Mention the flight length, that it was noted onboard, and that the lack of IFE significantly impacted the experience.
If the first response was vague, reply again and ask for escalation. Lufthansa often caves only after the second or third message.
Fair? For 14 hours, I’d say at least some miles or a voucher. But you won’t get it unless you explicitly ask.