Percent is all that matters when you are dealing with scale. Unless you are simply looking to fuel your own personal fanboyism, then sure — look at the raw numbers and make any physical comparison that helps you sleep at night; be it PS4s, duct taped game cubes or frontier style covered wagon wheels.
still: AMD vastly improved the efficiency with RDNA 2.0, so:
the real world performance of GCN 1 TFLOP vs real world performance of RDNA 2.0 1 TFLOP.
In other words: a dev can do with 0.5 gcn Flop not very much.
But with 3 RDNA 2.0 flops he will be able to do MUCH MUCH MORE! So, any percentages difference in those is NOW with RDNA 2.0 much bigger than with GCN, since GCN wasn’t nearly as efficient as RDNA 2.0
there are comparisons with GCN vs RDNA 1.0 on PC and even there the difference is huge, and now with RDNA 2.0 the difference is even bigger!