Google “petal rotor” to learn about that rotor type. As I understand it, the wave style outer edge of the NC rotor is for styling and supposedly to aid cooling, but not to intentionally cause pulsing. It sounds like the shop is throwing out excuses to make you go away.
The NC rotor should not pulse. If it’s not warped, I’d suggest cleaning it well, in case it has contamination in one area.
I once slightly bent an NC rotor during a tire change, which of course caused a slight pulsing during braking. As for “looking” warped, I could not see it or measure it, but it was bent. I replaced it with a used rotor from eBay and problem solved, meaning no vibration or pulsing at any speed. My other NC does not pulse or vibrate either. What you describe is not normal. The shop needs to address this or get another rotor.