The district office is originally the competent decision-making authority here and merely uses the construction experts of the municipality for professional evaluation preparation, but decides itself (i.e., not only as a reviewing instance). Usually, remarks from the municipality are interpreted as a recommendation and are followed - here not, because the development plan (in my view clearly) opposes agreeing to an exemption.
What the municipal building committee has to do with this is not clear to me: in such a constellation, it would usually only advise on the municipality’s own construction projects and on individual cases of private builders only if of public importance (e.g., supermarket). If I understand correctly, the architect would not have been present in the building committee as a relative, but as a committee member - and as such excluded from the consultation and resolution on this agenda item (due to bias).
After “considering all contributions of this thread,” I come to the conviction that your special treatment simply - even if the other buildings may seem like a mixed salad from your layman’s perspective - is the only one that stands out.
You are therefore requested to inform us by 13.09.2019 whether you wish to withdraw your preliminary building request, submit amended planning documents, or request an appealable decision
According to my Langenscheidt "Officialese - Plain German," this means: “based on (unless corrected) the records, we would have to reject the request” - and in my opinion in this case also with drums and trumpets administratively court-proof - “You now have the choice: either pay a hefty fee for this slapdown or pull the ripcord.” I strongly recommend the latter - especially if the mentioned date is also the deadline for corrections, because without consultation - preferably with the decision-making authority - an amended plan will not be adjusted sufficiently to obtain the desired approval.