AMs ZUIDWTC = SOuth, NO CS-to the detriment of so many who still believe that would be the place to go to (having worked the biggest part of my working life for that city-I would not do that anymore). The sector Schiphol Airpt-AMS CS now only sees very frequent ´airport shuttles/sprinters, with all stops.
Note that the old-style BeNeLux is now limited to ROTterdam-Brussel. But the ´hispeed´ sector RTM-S´hol is since many monthes partly under repair, has speed-restrictions and this is to continue for some more time to come too.
It IS also a NS-INTERNAT train on the NL-part, till border, where NMBS takes over, its a common ´enterprise´, And yes, there are different fares and several local fare-offers are not accepted-so in effect its seen as a ´premium´ service for ´premium´ fares=higher (not that much though and there are also cheaper advance offers). Others will probably have more finer details and corrections to this. So its not at all what you seem to suspect: some new competitor offering budget prices for a competing service. In fact to relieve overcrowding extra service was really needed at peak times.
For really cheap fares between those places; FLIXbus, also often nearly as fast.
