Sounds like a question of how much you're willing to spend for a certain volume of material, and what you want that material to do.
I'd equate it with getting an alcoholic drink from a bar that doesn't cut it's drinks with water (more expensive, better quality) vs. one that cuts (cheaper)
Foods with fillers [cheap] (especially dog foods) vs. high quality brands (less fillers)
24 karat gold vs 10 karat gold
It all boils down to: you need more of the cheap stuff to have the same effects of the more expensive stuff. You need to drink more cheap [cut] booze to get inebriated, feed more cheap food to get proper nutrition, or give more cheap jewelery to please the wife!
With the mix you get some more or less inert stuff that won't really harm anything, but doesn't help any either. Topsoil will fill the space, accept amendments, provide a home to new biologicals, and grow stuff eventually, but compost comes preloaded with all the goodies.
You get what you pay for, now you just need to pay for what you need!
Most commercial grade "compost" is a mixture of wood chips and cow poop. While both of these are technically industrial waste, these two ingredients are relatively benign (downsides for woodchips: allelopathic effect (a sort of natural herbide), acidic, sucks nitrogen out of it's immediate environment (the opposite of what you want for a lawn). downsides for cow poop: usually from a really gross feed lot where the critters are heavily medicated - and that medicated stuff is still in the poop - sometimes including deworming stuff which can kill your earth worms)
To re-iterate: I think wood chips and cow poop are **relatively** benign.
Some "compost" includes the industrial wastes of really nasty stuff. For a company to dispose of their waste properly, they would have to pay big bucks. But if they put it into "compost", they can sell it. The past couple of decades have exposed some really awful things down this road.
Nearly all commercial compost sold today contains clopyralid. A broadleaf herbicide with a half life of 11 years. It just lasts so long and it ends up in everything. It passes right through the cow. It ends up in the wood chips. It is in the grass that is mowed and sent to the composting facility.
Home made compost, however, is 100 times better than anything you can buy. The problem is that the amount most folks generate is not much.
I could write lots more on this, but I need to rope it in and say ....
Topsoil is dirt (sand/clay) and organic matter. Lots of places make topsoil by mixing dirt with "compost". Sometimes it is actually the top six inches of soil from some field that is being stripped to put in houses. But be careful, that topsoil (or the dirt) can contain clopyralid or all sorts of other toxic problems.
I tend to try to build the soil rather than import stuff. If I do import stuff, I am very particular about the ingredients.
So the message I am getting is this: good compost is the better option. The compost/topsoil that I was looking at is priced exactly the same. I'm planning on getting it from Reliance Composting, who appear to produce decent quality organic compost (they started making to produce organic grapes from their vineyards). It is about $31 for 1m3.