Good luck getting the response out of LH you want, not going to happen.

Having said that;
- you are at least a bit...... too "I am entitled to, and do so or else.....", IMHO. Expecting to be upgraded just because there are seats available and you have a condition? Boy! If you need such a seat; pay for it. Just like everybody else does that needs it.

- you are misquoting the EU legislation. It does NOT state that they should've assigned you seating that allowed you to raise you leg. Actually; I wouldn't be surprised to find seats able to let one raise his leg in a totally flat position in 90 degrees from the hip were very hard, if not impossible, to find in eco class in many configurations and always have been rather aware of it back in the days that I could still fly eco as my syndrome amongst others leaves it very realistic that I can end up needing to do so as part of wearing a cast or can even end up injuring inflight and needing it. One of the many, many medical reasons I now only fly business.

OK, back on the EU legislation. It only states that an airline should try and find appropriate seating. Very open to discussion and basically not one you are going to win unless you escalate it up to the EU and even then. As far as the part you quoted; you were not denied a reservation or travel on this flight because of discrimination (as it basically boiles down to, as any airline can still deny when medically found unsafe), you were able to use specified airport and airline facilities and assistance was provided as stated in the details of regulation you yourself quoted. As this is a flight originating in the US, the ACAA also applies but again an airline only has a obligiation to try and get an appropriate seat there is NO guarantee that they must provide.

Airsafety does NOT care for symantics what is a condition and what is a disability. You yourself have told the airline that you have needs that require special assistance. As such you are labeled as NOT qualified to be seated in an exit seat row as you would most likely be a risk factor in case of emergency instead of somebody that should be able without any limiting bound (even "just" having your child on the flight is enough to be seen that way) to help fellow passengers escape the aircraft through said emergency exit.

Factly; the claim is wayyyyyyyyy too long, way too detailed, way too cluttered with non interesting stuff for any customer service to really get to to point. Good complaints are factual, to the point and are not short novels filled with "he said and then she said". Let alone the added drama.

While LH could've done better in theory, probably should've, you are having no shot what so ever with this letter IMHO. And that's not just coming from my dislike of LH (I'm sure some of the older FF folks on here might remember me calling LH Hellish Airways). If you are smart, you haven't sent this in and will seriously redo it. Keep it short, factual and to the point. Be realistic and fair also helps alot. Have the new version read by a few people that are not so emotionally envolved and even better;have experience with customer service work. Have them judge if it's readable and something that any shot of getting the real complaint across. Heck; take a breather yourself first, take some time, put this to the backburner and start on serious drafts when the first emotions have settled down.

I have quite a dislike for LH and started reading this thread taking a seat and almost thinking "ah it involves LH, they're guilty unless proven innocent", so to say. Long before I finished reading it my sentiment changed big time. You come across as a bit of an overly entitled person with a chip on it's shoulder that paints a picture that one is entitled to above and beyond when on happens to have a condition. Whether you are or not, I don't know. But you sure are coming across as one to me. It also gives LH every reason not to take you seriously and put aside your complaint if they'ld want to. And that's coming from someone that gave LH quite some outlash on here during my rantings about having a taste of Deutschen Grundlichkeit (on the other hand; did use this board and friends to vent and redraft my letter a few times before sending in a workable complaint).