You’d need to make sure you crop it to 1:1.414. You can enter that in the crop tool manually, and then save it as a preset, or add it via darktablerc - see:
But it is completely normal that printed material does not reflect the image 1:1, there is a finite precision when it comes to physical machines handling physical paper.
At 300 DPI, 3464x4950 pixels would give you 293.3 mm x 419.1 mm (so Adobe’s numbers were a bit off). As A3 is 297 mm x 420, this would mean an error of about 3.7 mm and 0.9 mm, respectively, or 1.2% on one side, 0.2% on the other.