People always say this, and I think it's just another example of not really understanding what's going on. It's not that this isn't true, but rather that the actual difference isn't super large. Yes, with fixed hardware you will have 7 years to squeeze out performance, and that will yield results... but most of those optimizations will carry over to PC development as well (and vice versa, what devs have learned in terms of Ray tracing will carry over to consoles next gen).
But "Much higher performance"? I don't think so. At least we've never seen it from the likes of pretty much ANY multi-platform game.