Well, if the architect is the client, then he is also the general contractor and thus only secondarily wears the "architect" hat. In classic architect-designed construction, the client is the client.
(...)
Sure. However, the leverage you have over a craftsman is usually vastly overestimated, especially when it comes to the shell construction and you want or have to finish.
Because what would be the consequence in this case?
The wall is wrong, and if you're not lucky or clever enough to have the floor slab done by a different company than the masonry, then the mason will not continue until this issue is resolved.
You just have to see when it’s worth making a fuss, namely substantial, construction-damaging defects... or when it’s only about having to shrink the kitchen cabinets by 10 cm, which is usually absolutely no problem, because base cabinets come in 40, 50, 60, 80, 90, and 100 cm widths. For an additional charge, I believe you can even get 70 cm from some manufacturers.
Starting a dispute with the shell builder because the kitchen unit measures 3.98 instead of 4.01 m... okay, if you don’t need to live in the house within the next 2 or 3 years, go ahead. Most likely, even courts would rule that changing the wall is disproportionate to the damage.