The Dura-Ace EX (7200) introduced Shimano’s EX concept which I understood as being a design optimised for the (then radical) idea of using 6 speeds, particularly with the new Freehubs. It has virtually no inner pulley cage plate and a clever ‘Hatch-Plate Mechanism’ that allows the chain to be removed and inserted into the derailleur without tools. Campagnolo’s Nuovo Record was famously bad at handling 6 speed cogs (with the change into top gear, just before a sprint for the line, requiring faith, hope and charity) - and Shimano aimed to do the job properly - using science rather than religion.
Despite all of this, I found the Dura-Ace EX (7200) slightly unconvincing in its claims to be the ultimate derailleur. It lacked the clean, lightweight, minimalism of the Dura-Ace (7100), the true, bomb-proof, design of the Campagnolo Nuovo Record and the slant parallelogram of the SunTour Cyclone. Any dropped parallelogram gear will wear more quickly than the traditional Campagnolo design - because it loads the parallelogram pivots with some torsion. Any design without a slant parallelogram will not change as well as a SunTour. Any derailleur with two springs working against each other will be prone to one of the springs suffering exhaustion and going out of balance with the other.
I once heard a story of how Enzo Ferrari came upon Audi testing the original Quattro at Imola. The Audi engineers showed the great man their five cylinder engine, their weird engine bay layout with the in-line block almost in front of the front wheels and their radical four-wheel-drive system. Enzo Ferrari asked if he could take it for a test ride - and the Audi engineers agreed. Afterwards they eagerly asked him what he thought, and he is supposed to have replied that he could not congratulate them enough on the brilliant way that they had solved all the problems that they had caused for themselves. There is something of the Audi Quattro about the Dura-Ace EX (7200).
The Dura-Ace EX (7200) went through 4 generations:
This is a, very nice, example of the second version described above. Some key features are: