At an annual income of 40,000 EUR, there is about 1,100 EUR EU pension. 40,000 EUR annual income does not quite correspond to 2,100 EUR net. However, one saves one of the two cars, so at least 500 EUR per month. The gap is about 500 EUR per month. Wow. I would say a little less money to save. There are additional tax advantages for the other spouse due to joint assessment, so the gap is even smaller. If there were any professional expenses, these also no longer apply.
Otherwise, karni is right: There are two things, being right and getting justice. The BU only covers the case of being occupationally disabled but not totally disabled. Yes, those who have burnout, if anyone should acknowledge it, are not suddenly healed just because they work as a warehouse worker instead of as an office drone. And yes, I know, the BU also pays in case of full disability, but for this case you have the state EU pension.
I think you can also live well on a salary and if an EU pension is added, then that is a bonus. In most countries in the world, there is no such thing as BU insurance at all or at most as a niche. Many professions in Germany are either not insured or only insured at horrendously high rates. Many BUs are also only temporary, i.e. you are BU for a few months and then either healed or dead. The case that someone becomes BU in their 30s and the insurance then pays mid five-figure amounts every year for over 50 years is extremely, extremely rare.