If rankings are skewed towards gc guys, it’s probably because winning gc is the hardest thing in the sport. If it wasn’t, everyone would do it. If there were a way to make GC more open to guys like Sagan/Gilbert, not to mention Ganna, maybe it would be more fair on them; Kelly and Moser had to take a LOT of time in sprint bonuses and TTs to take their GT wins.
GCs are also time consuming when you consider the altitude training and then the rest period after, though I suppose those riders can also clock up good points in the one week warm-up tours like the Dauphine.
Alternatively a rider placing well in most classics can mount up the same points in the same time (GVA iirc was high in the ranking some years without ever winning much) and then you get the likes of Demare (2020) and Philipsen (2021) accumulating high scores from 1.1 races that usually end in sprints.