How bad is the seam on my quartz kitchen countertops?
Actually, I noticed two problems with your countertop. One, the gap does seem too large for a stone countertop. Two, the seam is perpendicular when it should have been cut and fitted at a 45 degree angle. The edge, or bullnose would fit together much better if cut and fitted at 45 degrees.  I suspect this was stock material installed by someone not equipped to do it properly.  Normally, the joints would be precision fitted at a 45 degree angle at the stoneworks before installation. The joint on a quality countertop would be exact, epoxied and polished.  In your case, there is no real, easy fix. The gap would have to be filled and sanded. Then the surface would have to be polished to bring back the original finish.