Anyway if you have nothing invested today and you can choose from the green lawn then the picture is a slightly different one.
Used lenses are great, issue is if you really can get the ones you need at the time you want to buy. And this does not happen too often. Sure you can safe money here and everybody would be a fool not to do so, but if you compare with the complete investment of say between 20-30k$ (or even higher) then the saving of say 3-5k is kind of becoming much less important.
If you have already a system and would need to sell this in order to buy into a new system, then it becomes much harder of course. And more "expensive".
But I cannot help myself that I am getting more and more fascinated with the simplicity and ergonomics and assumed quality of the S System - as you can see from my change of mind