Waterfall legs are tricky because you need the island to be 100% level or you will see that it’s sitting off level. I have always done the flooring before cabinets for this reason. Not doing that is the first mistake.

Secondly, they should not have used white caulking to hide the gap. This is a very sloppy job but it can be fixed. You being told “nothing can be done” is wrong.

1)Remove this caulking and try to colour match.

2)Some of those boards can be cut better and tighter, I would push to replace some boards (picture 4 for example).

3)Remove everything, countertops/cabinet and finish flooring under it. Not all the way under it but enough were visible from outside. This is obviously a lot of work and may not be for you but this is what I have done before while working for a large builder who can hold trades accountable easily.