While I have diamond ground some grades of carbide to very fine,sharp cutting edges...and cut very fine finishes with them,thats not the general rule with carbide.Those fine edges are fragile.If they chip,surface finish goes bad.
For durability, typically a "sharp" new carbide insert comes with the actual cutting edge radiused in a way we might consider "dulling".It might be a .003 radius.
That does not work well for taking light cuts. The cutting edge may smear along the surface,or occasionally dig under it.
When using carbide inserts.its usually about making money.Look at the speed and feed charts.I found I often got better results with carbide taking a fairly heavy cut with feeds (lathe) up around .010 or .012. The cutting edge is buried solidly under the chip. Another benefit was chip breaking. No long,stringy chips!! Curly popcorn!. Now,thats in steel but my point is,without a special grind,carbide is not always best for light scraping cuts.
(They engineer carbide inserts for about any purpose.There is a "right" insert for the job.But that may not include neck turning reloading brass.
If I had to choose a cutter for neck turning,I'd use high speed. And I'd grind it myself.
High speed can be hand stoned quite sharp. A fine india will do.
Brass tends to suck the cutter into the workpiece. An old trick is stoning a little negative rake on the top of the cutter.