Building drainage drainage plan

Hello dear forum,

attached you will find two pictures. One is the drainage proposal from our civil engineer and the other from my gas-water installer. The civil engineer wants to lead two vents over the roof because he believes that otherwise it will lead to problems. I personally prefer the solution of my installer. Only one vent over the roof. If I interpret DIN 1986-100 correctly, there is absolutely nothing against that.
What do you think? Is there anything technically speaking against it?
As can be seen in the photos, the two versions!

Many thanks for your help

Hello dear forum,
attached you will find two pictures.

Hello dear questioner, you are welcome to provide more context.

By the way, these are more ventilations than air vents (but actually both). Without air supply into the pipe, wastewater does not drain due to the resulting negative pressure. In one version, I don't see a branch ventilated at all? That would not be okay. Optionally, an internal ventilation is possible there, but if that can be avoided, I would never do it in my life. Once bite the bullet and have the few extra euros for the roof-guided ventilation installed. Wastewater "flows" better through the pipe that way.

In variant 2, the bathroom on the first floor is connected to the drainage of the ground floor, and the ventilation is routed through the roof at the bathroom on the first floor. I’m not sure if it’s a good idea to place the only vent "behind" a downpipe. With the architect’s variant, you play it safe.

That is clear, but he wants to vent both lines. I would prefer to install a vent over the roof as shown on my plan with the blue line. There is already a shaft there. Otherwise, there would be a second boxed shaft. Isn't that enough as I think?

Isn't it enough the way I think?

We cannot follow most of your thoughts with this small detailed excerpt and otherwise zero knowledge about your house in context.