I can’t see that point making any sense. A passenger who travels to France on the ferry and drives onto the Netherlands is checked by the PAF on entering Schengen; a passenger who flies to Köln and gets a train onwards is checked by the Bundespolizei. Why would the Koninklijke Marechaussee suddenly be dissatisfied with the PAF for travel by Eurostar? If someone is wanted they can be flagged on the Schengen Information System and the PAF will see that when they scan their passport.
Indeed, I think the message from NL has got a little garbled. It is a feature of the Schengen agreement that all signatories accept that frontier controls are done on entry to Schengen wherever it is. This is the most remarkable feature of it, eg. the Dutch have to rely on the Poles checking properly at the frontier with eg. Ukraine, the French from the UK, the Italians from Libya etc. etc. They are allowed to add their own controls on entry to NL in emergency circumstances (as the French, Swiss and Austrians have been doing on the Italian border for some time because of the migrant situation). So this concern about the PAF is probably something to do with Dutch domestic politics rather than Marechaussee....
Whilst I am here, can I let you know of a new horror that ES seem to have instituted at Lille Europe which I ran into last week, which is that they now let passengers for the next train
and the one after that checkin and go through security simultaneously -- thus making the 30 minute check in very challenging to deliver. For the 1835 train last week, the check-in didn't begin until 1805 and the departure hall was eventually quite full. I was one of the last to board (at c.1832) and had to run down the platform to get to the right end of the train in time. (If the ES trains are late from Lille Europe, they miss their tunnel slots). Some of the 1835 passengers were left behind, I think....in a departure hall full of people for the 1935. And my seat had been given away to someone else as they had assumed I was a no-show. It's great when they keep on finding new ways to keep their passengers entertained! Lille used to be so easy to use.