Meh. I don't think many (meaning any) luthiers have built as many excellent and highly praised instruments as Paul Reed Smith, and his nut slots are like canyons. It's all about what works, not what "conventional wisdom" says works.
Now, having said that, I'm seeing a lot of tuning problems (related to the nut) on PRS guitars, but Paul is no longer involved in the building process, so that could be a factor.
In general, we see really good setup on the Artist Series, but one would expect that in a $3,000 to $5,000+ guitar.
However, there's always exceptions. My colleague has a brand new PRS DGT with open (McCarty) tremolo ($3,800 retail) and it won't stay in tune. He is planning on returning it, so accurate setup is not guaranteed, even in the more expensive instruments.
We could easily correct the setup anomaly, but he is disappointed in the sheer principle that you cannot play a $4,000 guitar without a trip to the Luthier.
The guitar pitches sharp when the tremolo is used or when the strings are bent, so it's clearly binding in the nut.
When he contacted the PRS Tech Center (PTC) they told him (paraphrased) that an open tremolo is a "novelty" and if he wants a guitarvthat will stay in tune they recommended a CE 24 Blacktop Fkoyd Rose.
But, TBTH, I'm seeing a lot of tremolo equipped Fenders that won't stay in tune. Our local Fender warranty guy is busy with a 3 week backlog.