The Vienna Instruments are not 20 years old - the original software running the instruments was Gigastudio, an early sampling platform I still have nightmares about. Vienna Instruments came out much later and was a great advance that has steadily advanced more since then. Anyone who thinks Synchron or Vienna Instruments software are difficult and unintuitive should try a moldering copy of Gigastudio and write back from the Institute from the Criminally Insane which they will soon be imprisoned within.
Synchron exists mainly to provide people with a baked-in reverb that uses the hall the company acquired and records scores in. This is a little ironic, since VSL was originally touted as being great because you could use it with any reverb of your choice instead of being locked in to one - like East West Quantum Leap Orchestra which was its main competitor originally. Now, the Synchron system does the same approach (with much better sounds of course) using the acoustics of the hall that the instruments were recorded in. The player is excellent of course, but the previously listed advantages of Synchron over VI are non-advantages practically speaking, because VI can do anything in music. What more do you need than that?
I have been using it since it first appeared and evolved my own system somewhat like what Holgmeister mentioned, customizing all the setups of patches and incorporating MIR when it became available. The great advantage of VI is that it allows you to totally construct your own instruments from the patch level with incredible ease. I have never even once used the massive already set up presets or even matrices. I've always had the attitude, why load a dozen short note articulations when everything in a piece I am playing is legato? So why load every possible sound the instrument can make instead of construct an instrument tailor made for your own composition, and therefore ideally tweaked for the music? The great thing about VI is how you can create everything from the ground up for your orchestral setup, including the characteristics of the hall or reverb that are radically changeable. It is the ultimate do-it-yourself sample library, even though it is based on the masterfully played and recorded instruments that make up the articulations.
This is not what everyone wants of course. Many people want everything set up for them in advance and that is what Synchron and other similar libraries today are designed to do. And one can use it in any number of ways, but I really take issue with the concept that Synchron is new and up to date and Vienna Instruments is old and out of date - that is total bullshit, because VI is based ultimately on the real deciding factor of any sample library - musical performance of great players. That is front and center with Vienna Instruments in the absolute purity of the Silent Stage which gives you total access to every single note of the millions recorded by VSL. And the player allows total control of how you use those notes, how you control the parameters, and you can tweak easily the controls as well.
In short the Vienna Instruments is a true masterpiece of software engineering and the idea that it is old-fashioned and out of date is ludicrous. Synchron is another approach to playing the instruments using baked in reverb, and very well designed. But it is NOT superior, just a different approach, and I really think this downgrading of one in comparison to the other is just plain stupid.