The TE is not being "accused" here of wanting to build a dormer, but his illustrations clearly show a ground-floor "bay window" which actually is none. A bay window would be a shade-providing projection of the upper floor above a rear facade on the ground floor that does not protrude. In a way, the TE consistently calls an area on the upper floor a "balcony," although it does not cantilever but rather uses the roof of the already mislabelled dormer.
Development plans are not to be softened / overridden by simply renaming the things one desires in an exception-compliant manner according to the popular misuse of the terms. Nevertheless, the municipality goes too far with its building envelope specification here, and if, in return, it is generous with exceptions, this saves a lot of court costs for challenges to the development plan.
By the way: the core building envelope without exceeding it allows a main building here in the form of a replacement villa with 10.00 m edge length corresponding to approximately 160 sqm of "living space." Has already clarified whether an appetite for more would be financially covered? Countless builders have to "make do" with these dimensions without suffering from the stinginess of their rooms. 46 sqm living-dining area (plus kitchen!) is also not a "standard (sine qua non)" in a dual full-income household.
If one starts as a lay planner with a 10 x 10 m frame as a felt "100% = not too much" and divides it attractively, the result regularly is that it is too tight in at least one corner and extensions seem necessary. Usually, just for the "thorn in the side" in the form of the single-flight straight staircase plus dining area in the same room axis, it is necessary to equip the starting square with a forward and backward captain’s dormer. Not infrequently, a corner "bay window" is added to combine building services, wardrobe, and elderly bedroom. And suddenly, the replacement villa already has 180 sqm, and the builder still feels that nothing is really too much. Until the price is mentioned—then the cutting cascade begins.
Just consider letting the market share of house models in the Passat class speak for itself and conclude from it that the providers are well acquainted with the reality of the average non-Rockefellers. This size class is already "no longer understatement," and certainly no social housing anymore. This calculation cannot seriously "work without additional bulges." Causing 20 sqm of extra space as a lay planner costs 60k more house price and thus significantly more than a full architect’s fee. So much for the topic "saving by pre-working for the building application drawers."