It's not horrible; the whites are some of the most difficult seam inconspicuously. I'm betting that's not factory color match adhesive.

Place a straightedge over the seam please. It shouldn't have a gap and if it rocks, the pieces are out of plane to each other and the bottom of the seamed sides are touching, making it impossible to pull the top of the seam together tightly.

The sink can be dropped and the seam sawn apart fairly easily and mess-free; I've done this. Put the pieces on plane, use factory color match adhesive, and pull it together with Gorilla Grips.

How large is your island please?

looks pretty good!

Joseph, the countertop is around 7 to 8 feet long by 4 feet wide.

I would be upset too...have you communicated this to the company you worked with? Maybe they can at least give you some money back. I agree with Beth H, it sounds like the quickest fix would be to remove and replace with some more dull such as gray.

yes, the close-up pics it just jumps out at you but in this picture, I have to search for it. Most people will not be nose to stone in your kitchen staring at your seam.

I've sure seen way worse.

In both man-made quartz, and natural stone, a single slab is big enough to cover an island of your size. Your builder wanted to avoid the hassle of - moving a whole slab (it's incredibly heavy) - and the issue of moving it through the house to its eventual location. He saved money and labor at your expense.

At that size, there doesn't have to be any seam in that island. 32SF x 18lbs. psf= 576 lbs. That's less than 300 lbs. per guy with 2 guys.