I though about a machine to grind it level but that would be dusty unless its done wet and then you have dust when it dries, and unless its visible and huge gaps let it be, all concrete has low spots that will pool water even though it looks like glass. I too would let it be unless its a huge noticable thing, i dont think it will be an easy fight. Look into self leveling and can it tolerate driving, if it will maybe see if the guy will self level then seal it with something as that stuff looks like grey epoxy i beleive.
I have used one of these concrete grinding machines.
There are two basic kinds I know of, possibly more. The kind I used is called a "scarrifier" which is obviously not the same as the tooth-like attachment on a box blade or drag. They are very dusty and remove a very light layer of concrete by striking it with metal blades. Sort of the size of a lawn mower, but much heavier.
The surface finish they produce is coarse, almost like the concrete has been hit hard with thousands of small hammers about 1/8" in diameter. They can shave possibly 1/32" from concrete in one pass, maybe only half of that. The concrete turns to dust. I had a small "mound" of concrete in an otherwise flat floor, about 3" high and 12' in diameter. It took three days to get this to an acceptable point of maybe a 3/4" mound centered in the same place. You have to be careful to get it evenly ground down. Too many passes in the wrong place and you get a groove.
The second type of a machine is more of a polisher. Tt is used to produce Terrazzo-type floors. I am not sure how much material it removes, but I don't think it is the one for this situation.
* * * * * *
I will never again have concrete flatwork done by an outside contractor with out a flatness specification in the contract, and a measurement of flatness before payment.
I think you may have to learn to live with the surface you have, or, if you can accept a raised floor, pour a 3" pad on top of the one you have.
If you can't, tear it out and start again is the only realistic way of getting it flat.
* * * * *
I once had a contractor, after 18 months of trying to fix a serious problem tell me he had insurance, and that I should call them. Don't fall into this trap. The insurance company has done this thousands of times, you have only done it once. They will tell you what they are going to do, which is usually nothing or a very inexpensive fix, which does not work.
As soon as I heard that, I called a lawyer, who called the insurance company and told them what they were going to do. They didn't like this one little bit, but after a lot of wrangling they settled for $80k, which was about $70k higher than their first offer. If you do not have a lawyer, they will never seriously negotiate with you.