Construction costs are currently skyrocketing

In relation to salary, building is even cheaper nowadays than 20 years ago!

D is not only the Lake Constance region.

As I understand from your graphic: "Affordability Index" 2000: ~115 vs. ~135 2020.
Your DB Research figures also refute your claim. Since the observation period, house prices have outpaced income.

Regarding the topic of personal effort, I unfortunately have to agree with Durran. Whether he really followed through like that, I don't want to judge. However, in my opinion, the message is the right one. People in Germany, in general, are no longer willing to make sacrifices. No one gets anything for free here, and if you prioritize spending a lot of time with your family, you simply have to buy the services. Arguments like having two left hands, but then you start sweating, or the torn toenail are, for me personally, often just excuses. Talent aside, from a motor skills perspective, every person is probably talented enough to be able to do simple work on the house themselves.

the principal statement

What is not taken into account here are the subsidies like BAFA, Baukindergeld, etc....