I would hope Zen 2 is more than 4x the performance of Jaguar... Otherwise console manufacturers aren't getting bang for buck.
It depend on what kind of customization they will do with zen 2, there is a rumor that it's not full Zen 2, instead a cutdown L cache and downlock core speed. I also used the CPU performance comparison between Xbox SX (Scarlet) CPU with Xbox One X mentioned by Spencer and by Xbox official. Phil said the jump from One X to Series X on CPu is around 4 times. I guess PS4 pro to PS5 will be even bigger due to Xbox One X CPU is faster than Jaguar on Pro.