Vitus 980 is listed as being lighter in the published data, but if you look at the actual wall thickness, Vitus 980 is the same or slightly thicker in all tubes, meaning it should be slightly heavier. One of the reasons the published figures are lighter for Vitus is because they do not include the weight of the head and steerer tube in the data. The metric tubing is also slightly smaller diameter for some of the tubes. Finally, the lengths of the tubes in the tubesetset may be different. In frames of the same size, I would expect 753 to be lighter.
As for the whippy reputation, the Vitus 980 Peugeot frames were certainly too flexy for my personal liking. Curiously, frames made from Columus SL were more to my liking, despite having almost identical wall thickness dimensions. I attributed the difference to tube diameters, particulary the fatter downtube, but maybe there are some additional factors such as longer butts, frame geomtry, construction, etc.