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> For final grading I saw the excavator trucking out what looked like native soil and trucking in rocky soil.

They sell the topsoil and replace it with cheap (rocky) fill. Every. Time.

I'm unable to discern what the OP means there, but any slab on grade (including driveways and pathways) is only as good as the base underneath so that absolutely should be well compressed aggregate and you may have to pull out a lot of soil to fit it if conditions dictate. If anything is below grade, there should be a permeable drain pipe below the bottom grade at the footing, and drain aggregate running the vertical to prevent buoyancy as much as infiltration. If they tried to manage sub-grade moisture with the top soil, that is a disaster. The rest of the final grade may be specific to the drainage plan and geography, it is possible the soil needed amendment.

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