If you can get loam, a soil type that is about 45 percent sand, 25 percent clay, 25 percent silt, and 5 percent organic matter, you will still be adding lage amounts of what you already have, the mineral portion of the soil and very little of needed organic matter. If you buy "topsoil" you will get a large portion of what you already have, the mineral portion of the soil and little, if any, of the needed organic matter.
Organic matter in soils seperates the soil particles, loosens the soil which makes it more workable, allows more air into the soil and improves the flow of water throught that soil while helping to hold some in the plants root zone, and supplies needed nutrients. How much organic matter might be needed depends on how much is there now, you want about 6 to 8 percent. You also may need some "topsoil" to bring that area up to the grade, but that needs to be balanced with organic matter.

What to do sll depends on whether you demand instant results for a higher cost, or you are willing to take time and let nature do it with some help from you.

It's hard to recommend how much to remove and replace if we know little about the existing soil.

If you want to go the other way, I would have them break it up, and start adding organic matter, perhaps tilling in a load of compost yet this fall, and layering mulch over that if you can. You can't really go wrong doing that.

Before you add anything, send in a composite sample to your county ag extension soil lab and find out what you have in terms of nutrients, organic matter, and sand/silt/clay.

Note that when you start adding organic matter, and stop walking on it, it will begin to fluff up over time.

Whether you still need some topsoil is the big question. I doubt you can get 6" of lift without adding at least some imported soil. So maybe the answer is to loosen and amend the existing soil, then bring in several inches of good organic topsoil to bring it up to grade.

Hope that helps.