You totally missed the point. The point was that it doesnt make sense to use a more expensive iris pro cpu when you are adding a discrete card.
The world does not run completely on logic. That's why certain marketing tactics work. That's why you see HD 520 setups(and previous HD graphics generations) bundled with discrete cards that are questionably worse than the iGPU in performance. But Nvidia's and AMD's reputation as a graphics company and Intel's lack of(and bad drivers) drive them to use it. There's also a stigma related to iGPUs which is probably why even Carrizo is offered with dGPUs.
There's couple reasons to use an Iris Pro enabled GPU
-Halo factor
-eDRAM does help a little bit for CPU
Remember that the Iris 580 only have 1.5x the EUs of the Iris 540/550 and the 950M is about 2x faster than 940M. The Iris 540/550 have 2x the EUs of the HD520 yet only outperform it by 60%~70%.
You know the 1.5x number people are using are probably based on Intel's own slides right? That's over their quad-core, 45W, Iris Pro 6200 setup. Quad cores iGPUs are noticeably faster than the dual core ones because they have more TDP headroom.
There's about 30% difference between Iris 540 15W and Iris 550 28W(in real games, not synthetics that run for a minute and never run into power throttling). I believe additional 20% exists from a 28W Iris 550 to a theoretical 45W Iris "555".
Of course, Intel's expectation of "50% gain" is according to the footnotes, "best case" to say roughly. But 50% isn't unrealistic, because architectural enhancements of Gen 9 is somewhat cancelled out by front-end of the iGPU in a GT4 setup not really increasing over a GT3 one.
-30% as observed from Gen 8 to Gen 9
-50% more slices, which brings in less than 50%(how much??)
-Front end nearly identical(well, in SKL, GT4 front end clocks slightly lower than GT3)
-Memory bandwidth identical?
-Effect of changing from victim cache eDRAM to new setup in SKL
Glo, Iris 540 is not competitive to a 940M. It is barely before its 15W power headroom runs out and then it runs noticeably slower. It's ~30% faster according to longer-term SP4 tests than HD 520. 28W Iris 550 on the other hand(new Vaio, and MBP 13") would be.
These are not going to hit the market till mid-2016 (earliest), while Iris Pro 580 is technically out right now.
All the Iris Pro 580 parts are supposed to be "H1". I am guessing April. That's like 2-3 months away from a Polaris part. Iris Pro 580 is 50% better than Iris Pro 6200. Polaris and Pascal are 2x over predecessors. That means comparatively it'll be worse than Iris Pro 6200 would have been. Of course that's if 2x is uniform. Probably AMD/Nvidia will capitalize on that for more margins at the low end Iris chips are competing. Intel needed Iris Pro 580 last summer.