It's been a while since we had performance competitive CPUs from AMD, so some may have forgotten, but usually when it comes to CPUs, when they are close in performance they trade blows. Neither one of them is an absolute winner.
But ultimately, the most important thing for Zen is perf/watt. They don't even need the absolute performance crown, as long as it's close enough. Haswell level on single thread would be sufficient.
If Zen is performance per watt competitive with Intel, there is no way it's not taking some marketshare from Intel in server space. And even 10% of the server marketshare taken would be huge for AMD. While 10% of the server marketshare may not mean much to Intel, for AMD that would double their earnings.
Intel might be ready to cut prices, but there is plenty of profit margin there for AMD to slot in.
Also Zen itself on its own isn't particularly dangerous in the consumer space. Let's remind ourselves that the only reason AMD's APUs haven't taken off as they should have is because they were held back by poor CPU cores, and an old fab process.
We know AMD is capable of delivering a power efficient CPU even on 28nm, I mean look what they have been able to do with Carrizo, and that's starting from an inherently inefficient arch. If Zen is performance competitive to Intel, Zen based APU will absolutely dominate x86 APU market.. and that's not even counting HBM based APUs. Which would be a no brainier for OEMs like Apple etc.. Heck they can even offer custom-semi designed SoCs with all the features an OEM would want to differentiate their product. Intel can't/won't compete with that.
It's a big if, but if AMD executes well on Zen, they are absolutely on the track of reclaiming some of their old market share. And as I said, AMD doesn't even need that much market share to turn things around, because they are a much smaller company today than they were before.
Intel perhaps saw the writing on the wall, when they decided to lay off 12% of their workforce. In either case, these next 18 months might be really interesting.