Well, technically you're both right. It is over-supported, since the design code requires the structure to have some safety margin - which basically means you design it to withstand a force half again as strong as the strongest one you're likely to encounter during the ride's life time. With this "150 % reference force" as a basis, you design the structure to withstand that and then some, under the assumption that your materials are of a poorer quality than specified, just to be sure. Additionally, structural elements usually come in pre-defined sizes, and you always round up your theoretically required size to the nearest standard one. All this usually culminates in an end product that - theoretically - would be able to handle two or three times as strong forces as they are likely to ever be subject to under normal operation.
However, that's not to say those safety margins aren't required. A miscalculation here, a material fault there... if you had designed the ride to the bare minimum, it would be pretty likely to collapse or otherwise fail at some point. And juridically speaking, you don't really want to slack on the building codes either - one inspection, and your career outside the burger-flipping world would meet a rather abrupt end. So all in all, the ride is over-supported by necessity. However, it isn't more over-supported than it needs to be.