Agreed. MUC is a purpose built facility for Lufthansa which has been very well thought out and had the fortune of being designed after security measures/etc were updated.

FRA has had several different "band-aids" placed on over the years and is quite strange in terms of tunnels, trains, little corridors, stairwells- in fact the only stranger airport I can think of in Europe is LHR with its five terminals and bizarre buses that seem never to be able to be where they are needed on time.

I would suggest to any but the true masochist traveller to avoid FRA if they can- the one advantage FRA has is of course many more destinations and so if something goes wrong the probability of another flight being available within a few hours is much higher.