As as LH Senator (Gold) I concur that Frankfurt is not the best place to connect. However, we need to seperate what is the airport (Fraport) and what is Lufthansa’s issues. Some of the Senator lounges get really crowded at peak times; nothing is worse than MUC Schengen lounge which is dreadful at time (while the airport is brilliant!)
My gripe (as many others) is how Fraport organise between European Schengen and None-Schengen flights. Flights orginating in FRA require two security screenings when travelling to UK and Swiss destinations.
Lufthansa on the other hand is in my view one of the best managed airlines in the world. Just look at financial performance over the last years; the Swiss integration is a perfect example.