I would advocate for future funding programs, similar to the Baukindergeld, to take into account income and asset situations, as well as the number of children and, if applicable, local real estate prices in the assessment.
Of course, this makes the approval process more complex. Ultimately, however, the money would reach where it is needed.
That means considering KFW 55 or better as standard and distributing the money where it is really needed. Someone who has received the bank's approval for their suburban bunker should be able to manage without the funding anyway.