Others more knowledgeable will provide far more detail, but S Glass techniques were pioneered in the 70's - 80's as were many other technologies to "improve" glass tapers. It was , IMO, the Golden Age of glass. Generally, I see that s-glass designs are thinner in diameter and can be stiffer in action with more dampening ( less tip wobble). I have heard some say that it is closer to graphite in action. E glass has been around longer and, IMO, is more the norm in glass action and properties. Generally softer and wider in diameter, often translates into a softer flex. Yet there were many technologies out there , Phillipson & Peake and many others, who changed the feel and tapers and properties of glass. I feel that the "Tapers" are far more important than most people assume. I would agree with Jim Green, check an interview, that glass never really was given the chance to develop over many years different tapers. For example, there are S-glass tapers that are stiff or soft. There are glass(w/graphite) tapers that vary ... and e-glass tapers can be from clunky to silky smooth, IMO. If S-Glass technology allows for thinner, better dampened, and faster glass, then I assume that is what many modern anglers might lean towards - since graphite is the norm today ( while not so in my house). I think if you scan the posts here , you will find many rods from different eras and makers that are ideal in the fisher's hands- ah, it's the tapers.
Just my 2 cents ... others can be far more specific ... any engineers out there ... glass blank makers?