I would not accept that

That looks unacceptable to me. I don't know the arrangements you made with the fabricator, but it seems that you should have been able to get that length with a single piece. If not, the seam would have been better in the center of the cooktop. But I am no expert, so hopefully one will give you their opinion.

I wouldn’t accept that... it would bother me forever. New home builders do this kind of stuff a lot. You have to stay on top of things with them because they aren’t looking at details. They just want to get it done the fastest and cheapest way.

I plan on standing my ground and not closing until its addressed. Wanted to make sure I wasn't overreacting. The idea of having the seam in the middle of the cooktop is a great suggestion. The current placement is so noticeable, it can't be industry standard.

The issue is the seam placement and why they added on that small piece like that. When you mentioned variation in the pattern, that cannot be helped at a seam if the homeowner has not purchased book-matched slabs. So your complaint to the fabricator should be that it's weird that they seamed it there, with just that small piece. They should have either seamed it at the cooktop, or even not seamed it at all, since that counter does not appear to be that long and a slab would have been wide enough to cover it without a seam. The stone is very pretty in any case.

They used leftovers from other projects to save (themselves) money. Of course, that’s just speculation on my part. Since this isn’t a custom build, though, I’m not sure what recourse you have if any. My advice? Go over your contract with a fine-tooth comb before making any demands of the builder.

Before purchasing granite, take complete measurements of your counter sizes so you will be able to know how many slabs you need. I shop at a stone yard which has their own team of installers who come to the house and do a diagram of each counter area. A good experienced fabricator will plan all the cuts...and will put any seams in an unobtrusive location, such as where the sink or cooktop will go, for the least visible and closest matching parts of your slabs. My kitchen required three slabs to provide enough material for the longest runs of counter to be seamless. Leftover material was cut to fit two small cart-tops and a larger piece to sit on one end of the butcherblock island counter. All exposed edges are polished. Additional leftovers can be used in your BBQ area or outdoor serving place.

What type of construction is this? If this is a tract or developers home where you purchase the entire home and property on completion you may not be able to refuse to close, as the contract will be strongly in the builders favor.

The block that was chosen probably wasn’t wide enough to cover that whole back wall. Long slabs are really expensive, so seams are common when you have a really long or (in my case, complicated) layout. Lots of times, the seam is placed around the stove or the sink, where a natural bread can hide it. Personally, I don’t think this is the end of the world - it clearly delineated one zone from another and is only noticeable when you are close up. If it really bugs you, you can think about replacing the slab along your back wall - just make sure to talk with your fabricator to understand what is possible and what is not.

"Just curious, is this industry standard?"

As far as the quality of the seam, adhesive, and movement match, yes. It's well done. I'm sick to death of Houzzers thinking that somehow fabricators can just magically make stone movement align perfectly.

"Does the seam even need to be there?"

That's a tougher question. I'm willing to bet your builder has kicked the crap out of the prices he pays the fabricator. This makes the fabricator try to utilize every slab without creating expensive remnants leaning on a rack. Sometimes you can get away with this, sometimes you can't. From what I've seen and read, you're not in a very strong position to bargain. If the fabricator can make money on the do-over, he'll be all in.

Those look like 24" deep cabinets under your island with about a 7' span. That's way too deep and far for unsupported 3cm natural stone. If that's the case somebody's gotta do something about that. No arguing with page 3. I'd suggest a length of 2" square tube steel painted flat black and set in 6" from the edge or so with tabs welded to the ends to attach it to the cabinets.