Well, the 997 isn't exactly a new platform either. Regardless of whether it's a GT3 or not, the 997 platform debuted in 2006. I'd argue the 458 was actually a generation ahead of the 997.

Comparing cars is pretty difficult because they are often on different life cycles. There is overlapping in performance and superiority. Even a 2 year gap can be massive in terms of technology. It could be the difference between Al vs CF tub. It could be the difference between F1 and DCT. It could be a lot of things.