I’m a bit confused - Snapmaker to my knowledge always claimed 400x400x400 for the Artisan - where did you read about the plus you expected?
As for 350mm instead of 400 for 3D printing: This seems to come from the dual extrusion head, where one nozzle cannot reach the full 400 mm - same for the dual extrusion head on SM 2.0 - it reduces available build volume. I assume(!) that if you attached a Snapmaker 2.0 single extrusion head (which I believe would need an adapter to the quick change system) to the Artisan, you might get to 400 mm also in 3D printing.
All this is only assumptions - I never planned to buy Artisan, so I followed its development only out of interest without deeper thinking.