Overhead/waste in PCs regarding gaming graphics hasn't been nearly like it was back in the bad old days. In fact, you have two distinct areas to think about :

CPU : In this area, a PC usually has quite a bit more going on. It would get really boring to go into all of the details, but suffice to say, unless you're really running barebones with absolutely nothing in the background, a console OS will have less happening that demands CPU attention. Result : on consoles you can generally get away with a good bit less CPU power, though sadly this results in making 60fps titles hard to do unless you really cut down on API and make good use of GPGPU functions.

GPU : Vastly different. nVidia and AMD have made massive strides in their drivers and architecture for the pursuit of efficiency. Back in DX9 and earlier, draw calls were a massive roadblock to performance, but multithreaded drivers are a thing now, and newer/better DX versions make the gap tiny between console and PC. DX12 and Vulcan eliminate any real difference at all. This isn't a new 2016+ era thing either, there are TONS of games where an i3 and 750ti (a dual core processor and a GPU virtually equal in power to the 7850-level APU in the PS4) meets or exceeds console performance easily. See : 720/900P games like BF4/SWBF that run at 1080P on 750ti with console detail settings.

TLDR : It's not 2009 anymore. Consoles aren't any more efficient than PCs in using their GPUs effectively to any substantive degree.

No it's not logical.

Consoles tend to "wall in" their resources to confine their OS's so they don't consume resources meant for running games.

Fact of the matter though is the PS4 and Xbox One's OS's already reserve more resources than what Windows 10 would use.

Not exactly. Microsoft is still retaining full control over the platform.

The Xbox uses a Windows 10 Core+Xbox OS anyway with Virtualised OS's like the Xbox 360, they have multiple OS's running in tandem, backed by Direct X, it's more PC like than people realise.
And that's not exactly a bad thing either, the PC is a massive market that would be silly for a company to ignore.

In-case you haven't noticed, but AMD released a statement that the high RX 480 power consumption wasn't not by design, they will be issuing updates to rectify it.
The reason why it's not as big of a problem as it might have been is because PC power delivery is typically over engineered anyway.

Secondly... You are only looking at what "adds" to power consumption, but you TOTALLY ignore the power savings an APU will bring, like removal of 4-8Gb of GDDR 5 Ram and extra memory controllers, consolidation of CPU and GPU L1, L2, L3 and some cases, L4 caches, internal chip buses will be shared, consolidation of the power delivery (Mosfets etc'.) and chipsets to handle it all.

Not only that, but the APU will come after the RX 480, which means a respin and AMD learning about the Pro's and Con's of Global Foundries 14nm process, allowing for further power savings due to fabrication maturity.

They could also throw in something like a resonent clock mesh so that power could be recycled instead of wasted too.

As for Power Supply's... They typically offer more wattage than is typically needed. Why is this you may ask? Well it's simple.
As a Power Supply starts to get older, the maximum wattage they can reliably supply begins to decrease, this is due to capacitor aging, consoles are meant to be around for an entire generation, so it makes sense to over engineer that important piece of hardware... And it is not representational of how much energy a device will consume.