It's always a bit risky to assign to rating division as to which openings work when...
Sorry if I didn't get my point across clearly enough - what I meant was that if you are playing in a major tournament or Open, where your opponents can see your games and prepare specifically for you, then it really helps to have another opening that you can play.
I did not say that the Dutch is unplayable (that would not only be a load of rubbish, but also arrogant) - I entirely agree that it is an excellent practical choice, especially as a surprise weapon. However, playing the same opening all the time is risky (unless you are one of the leading experts in your country

), but playing a double-edged, tactical opening all the time (such as the Dutch) when your opponents can prepare for you is even riskier.
I can recall from my early career, when I played the same opening (which was very tactical), many of my opponents started preparing for me and beating me in that line, so I made sure I had another defence to 1.d4 as well.