So you switched from a quadcore + dGPU to a dualcore + iGPU with no impact on your workflow....you might as well buy a MB which is even lighter and thinner...
That is the core of the problem...people buy a MBP because is thin when Apple does the MB that would have been perfect for them.
Both lines of Apple laptops are thin and underpowered for people who value thinness over performances...
I never said I still worked on that 15" MBP - it was far too slow for anything (I still use it for some web surfing though). Also, it is a dual-core machine with a dGPU that is far inferior to the Intel Iris iGPU. Actually, I do most of my work on a maxed out 5k iMac - I don't own a newer MacBook myself just yet. I'm using a 15" one at the ad agency I'm working at. Since the current machines are only dual-core, I'm waiting for the quad-core 13" ones next year before I upgrade my private notebook (which is used heavily for photo editing, hence the need for more power).
So maybe being a full time graphic designer, doing video edits, 3D Renderings using Cinema4D, ultra high resolution visuals in Photoshop and complex layouts in InDesign for a living simply isn't what you call professional use anymore. Frankly, I'm not sure what qualifies as "professional" by these standards.
I don't see the drawbacks everyone's talking about in the current 15" MBP (and, hopefully, next years 13" MBP). Sure, the actual render work is outsourced to our render farm, but apart from that, it handles everything I throw at it with ease. And it does all that while still being thin and light. So, it's the perfect compromise for me.
Don't get me wrong, I do indeed see where you're coming from. Compared to some of the competition, the MacBook Pro series is indeed a little weak on paper, and very expensive for the performance you get. But in practical use, it's just about perfect for me.