if I'm not mistaken, you have a wooden house, right? I don't know it personally, but I would think that it is inherently a different indoor climate and therefore difficult to compare.
A sheet of paper is airtight with respect to airflow, but not with respect to moisture transport. Which "airtight" do you mean?
He means both. The difference in masonry is maybe 1% between "bad" and "breathing" masonry (where masonry means monolithic masonry, wooden house, ETICS, etc.). So instead of 1-2% of the air humidity being released through the wall with the bad wall, 2-3% is released with the "breathing" wall. But that doesn't matter, since 97% or 98% through ventilation is practically the same.
Someone still has to write that walls without ETICS can breathe
I just came from my renovation site. I listened carefully. The walls even groaned because ETICS is going to be applied and they are afraid of suffocating ;)
Before our walls get short of breath, we ventilate very regularly. Poroton filled, 42cm, without [Kontrollierte-Wohnraumlüftung], built without [KfW] and energy consultant, no fear of open windows and doors
There is a reason why people feel very comfortable in some houses and perceive others as "stuffy." This has to do with the behavior of the occupants and building physics. The wall construction and the connection of different materials to each other (whichever) and the technology used for temperature and humidity control certainly play a role. Reducing it to one building material (wood or stone) is just as short-sighted as reducing it to "airtightness." It is the reduction paired with the fundamentally sounding statement that everything else is nonsense that I do not like. Surely, both sides work with metaphors that work more or less well. The process that a material acts as a moisture regulator by absorbing moisture and then releasing it back into the room (not through the wall to the outside) by calling it "breathing" is an illustration that is not far-fetched and at the same time literally nonsense.