i have a million questions but i will start with....
WHY is there a seam on the side?

"i have a million questions but i will start with....
WHY is there a seam on the side?"

Built up edge to make the granite appears thicker. Sloppily done however.

Was it 2cm granite? because it already looks like its standard thickness?

Sure looks like 1 5/8" - 1 3/4" to me which would be (2) pcs 2 cm thick.

I could make that section much less conspicuous for about $500.00 or so if you were local.

"My biggest question is how do we fix this? Do we need to replace the entire slab??"

No, the entire slab doesn't need to be replaced, but you need a diamond burr and the only place I know where to get it is with the deluxe FillaChip kit which costs about $500.00. I don't even have one yet, but that crap lamination would damn near disappear if I did.

Joseph: Are those granite pieces that you epoxy-ed (?) in to repair missing chunks, and then ground down and polished? Looks great!

Sammy:

When I made the new sink cutout for that job, my saw blade bisected the original grinder slot made to hold the original sink clips. Nuthin' I can do but fix it, 'cause the new sink goes where it goes. The replacement stone is taken from the old cutout drops, shaped, fitted, then adhered in place with color matched methacrylate. I freehand them to near flush with a grinder, take 'em home to flush with a water bottle misted 60 grit, then polish.

If this happens on your job, I'm not saying a thing, because you can never "unsee" it if I point it out and you'll never find it if I don't. Look for the beginning of the arc to the right in the middle of the last picture or for the three larger dark particulates in each picture. And remember, unless you're scrubbing, your face is never that close to that edge.

Some are better than others:

Explain that you’re going to be reasonable and give them one chance to fix it, so they better get it right this time.

Glad you like it. 1/4" was a bit egregious for what was there, 1/16" or 1/8" was probably sufficient. As long as you are happy with how it looks. There was however, never a reason for it to look that bad to start with.

Excellent.

nice work. it looks better

Oh yes, so much better. Glad you got it fixed!