When comparing these boards, make sure to compare apples to apples! If you rode an NSR with no plate (or, say with a Donek AF plate or Vist plate) and a Kessler with a Hangl plate, the difference is going to be huge and the plate will make up most of that difference. I've ridden a couple of Kesslers with Hangl plates and man were they "locked in" and I've ridden one without a plate and I could skid it around trivially. All square-tailed GS's, 180 and 185.
FWIW I have no problem skidding my NSR 183 with the Coiler Magic Carpet plate around at will... in fact it skids around easier than pretty much any other alpine board I've owned. It's camber profile is in fact designed to allow it. I had a 185 that was one of the first dozen or so NSRs made... that one didn't transition from skid to carve and back as easily as my newer 183 but I could certainly skid and slarve it at will.
I'm of the opinion that the square tail vs round tail makes almost no difference when riding forward on groomed, at least on boards where the effective edge ends before you get to the tail. I've yet to see a square-tailed Coiler race deck where the effective edge went to the tail. If memory serves the older EX decks had edge length go to the tail maybe? IMHO the difference is aesthetic and psychological only, unless you asked Bruce for something unusual when ordering.
In any case the newer NSR's with V-Cam (Variable camber... a tailored camber that higher in the middle but flattens partway out before it decambers at the ends) are really great for edge grip when you want it and skidability when you want skid ability. My 183 has a 170 effective edge but but if you run it flat on its base on firm snow there is noticeably less than 170cm of base on snow due to the camber profile, hence the skid-friendliness. I never notice it when carving... even weighted down with a plate it makes quick, nimble, solid edge changes and the entire edge feels engaged from the get-go.
No idea if Kessler is doing anything similar...