About the topic of LH German market dominance and barriers of entry:
Source: crankyflier.com, topic of IAG-Air Europa Acquisition
I would focus on MUC instead of FRA. There are no slots available at peak (attractive) times, it has a new terminal co-founded by LH, and the city of Munich is blocking the construction of a third runway that the LH CEO has stated they do not need for the time being, at the same time that LH is moving planes and worforce to Munich. So yes, I consider there are entry barriers in the exact place where competition is most needed, as the LH monopoly has very high fares in what they themselves have called "premium" market. The government should help LCCs in order to lower fares for the average Joe.
Second, on the hub feeder flights like NUE-MUC. Yes, I get the point of these kind of flights. Yes, they have a reason. But does that mean that they should exist? Do we really need unnecessary, highly-contaminating (per-km) 20-min flights just so people can connect? I believe they should be forbidden, and this kind of low-impact, high-reward measures for climate should the ones that should be pursued. I find the sole existence of this flight to be outrageous...
Biz pax can no longer connect. So what? Take the train/car/bus like you would in any other European country. Any person living 1hr out of a major Airport in annther EU country would not even think of flying...
I remember the highly-criticised QR 9-minute flight in the Netherlands... well, here we have 7x daily 20-minute flights...
We all know that Lufthansa has a big presents in Germany and we know that they have a big parts of the slots at their hub. The question is just, is that a proof of manipulation or restrictions?
We really have to look at movements, are they limited, is the limit reached, or how would a restrictive policy work? There is now legal way to give LH an edge apart from them beieng the incumbent in regards to slots and nowhere slots are taken and redistributed as long thy are used.
FRA has a third parallel runway, movements grow considerable between the years. The limiting factor in FRA is terminal space and a new terminal is build. FRA, to the anger of LH, is actively looking for customers adding flights I do not see any restrictive policy to aid LH.
MUC has two fully independent runways, is at about 415,000 movements, should able to expand the number of movements and is growing (LHR has 480,000 movements). The do not seem to go after new airlines, but they are not discouraging. LH has actually a bigger influence here than at FRA.
TXL is in regards to capacity right to the wall, self limiting.
No other airport in Germany is in any way slot restricted.
The graph you show, does not account for the size of frame the Hub carrier is flying. At MUC and FRA LH is using a lot of big wide body frames, that can skew the picture.
I am fully of the opinion if some European carrier other than LH, wants to fly new routes they will not face any restriction. But they have to have the will to do it.