Actually in past extreme series was released near, and in some cases, before the mainstream. So in the past, when you paid a premium you got the best.
However, since they split the platforms, the extreme platform is released 1 generation behind in performance and soon becomes 2 generations behind. So only in the past you paid more for the best...in present if you want the best you buy haswell. If you want to pay 2-3x the price for a generation slower ips, an outdated platform, just to get 2 more cores so 5% of apps run faster then you get the extreme.
Fact is, if IVY E were same price as Haswell, I would still buy Haswell. Why would I buy slower cpu for 95% apps, and an outdated platform...unless it was priced less than Haswell.
Until intel resumes releasing extreme cpus near mainstream release, if you want the best for 95% apps, you dont waste money on an outdated platform, you buy the current generation, Haswell.