I just watched a good YouTube video that demonstrated how an inline parallelogram derailleur works, and how the slant parallelogram improved on the design so the derailleur follows the slope of the cogs.
But how did the old ones feel on a ride? Like if you had a Campagnolo Nuovo Record from the 70s, and it's clean & smooth, with a nice clean chain, smooth bottom bracket etc--how does it feel when you're riding and shifting? Especially since you're a rider from the future and you know how the newer stuff feels; does the old feel clunky by comparison? Or still very wonderful and smooth?
(I've never actually ridden on a bike with those old Campagnolo parts, just admired them from afar.)
P.S. Why did those Campagnolo Nuovo Record derailleurs stand so vertical? Was that unique to Campagnolo, or did all inline parallelograms look that way? If you look at this pic, the Dura Ace is shaped like the number 7--almost horizontal, then angling back 45 degrees--whereas the Campagnolo is just vertical: