A couple of years ago I was only given 6,000 Avios for missing kosher meal LHR-BKK in CW as GCH - 12 hour fiight. I couldn't eat anything at all, as strictly orthodox (OK crew did find me an apple..).
Crew confirmed it was catering error, as kosher meal was confirmed on their manifest, but said they didn't want to delay flight by asking catering for missing meal at 10pm.
Even after much argument and escalation they were unwilling to increase compensation.
I felt that was much too low, as was starving when we got to BKK (was planning on having dinner and beakfast on flight).
So 5K for FRA-LHR seems quite generous to me, especially if OP can eat other food...