Lu,
First, you keep referring to the 'pro-Robinson' site as if it's official. It's not. I'm guessing that the people who put up that site don't really understand the dynamic effects of a delta hinge either (which as you recall I tried to explain some time ago). I opine that they don't understand how the Robinson head works, so they assume it's the same as a JetRanger and think of them interchangeably--it's not! Most texts written for heli pilots don't go into the complexities of rotor heads with a natural frequency of anything other than 1/rev. Because of this, virtually anyone you ask about how a rotor works will tell you how the head works on a 206. While many helicopters may function this way and such a rotor model may be considered the norm, it is NOT the rule! And as far as the delta hinge is concerned, it is there irrespective of collective position or speed. It just means that an upward flapping translation of a given blade will cause a more negative feathering angle on that blade. The magnitude of its effect will change with speed and collective position, but its fundamental effect will remain the same.
As far as an experienced pilot noticing an extra 18° of control input, I think it's not too unreasonable to expect someone to notice, even with all the other effects (transverse flow effect, translating tendency, etc). That's because all these effects are present in any conventional helicopter. I'm not extremely experienced (having flown 300Cs, R-22s and a few A109s briefly) so I can't really attest to this, but I'm guessing those who have flown many types would surely notice such an abnormal control system. And as Arkroyal has said, I think this would have been noticed by pilots long ago...