Nope. This doesn't prove your point. It may in that XBO gained very little from DX12, but that doesn't necessarily mean it had all those features from launch. Here are some screen caps I took below.
You can see here that fast semantics, the low level variant for XBO was in preview until April 2014, May the following month they recommended that everyone begin using Fast Semantics. Prior to that XBO only had DX11.1, the XBO extensions added were for managing esram.
The remaining features, like Tiled Resources, Execute Indirect and such were added later.
In particular, and to the benefit of your position, executeIndirect (or at least some form of it) was introduced to XBO in May of 2014, titled New MultiDraw APIs -- this would be to replace the existing cruddier DX11 Indirect draws I imagine.
I took a screen cap, note it says similar to multi_draw_indirect on openGL. Unfortunately I do not have the technical knowledge to separate executeIndirect on DX12 from this version on XBO.
But I do see some main differences. Mainly that this version of Multi-draw is to relieve the CPU of batching work over and over again. Where ExecuteIndirect, the GPU is allowed to submit draw calls as well.
And I also know that a great deal of things can change during ExecuteIndirect, where with multiDraw with DX11 you are locked. And there's nothing within this API (at the time) that shows the level of customization that executeIndirect has.
TLDR; i don't believe XBO has had ExecuteIndirect, and didn't until DX12 was released onto XBO. It had multi draw, but I don't think it had ExecuteIndirect.
Continuing,
You notice there that XBO is also just receiving Async Compute, and is now putting Tiled Resources into Preview.
We're pretty positive we saw these features at launch with PS4. KillZone was already running 1 async compute thread as a launch title. I'm also pretty positive they weren't available for DirectX11.1 for PC.
Here is DICE's full slide deck:
http://www.wihlidal.ca/Presentations/GDC_2016_Compute.pdf
In your original question of whether it was there before or not, I believe this somewhat suffices as an answer:
I want to dial back a bit and flip perspectives to your side of the argument. Assume all of this did nothing at all. No performance gain. If the frame rate is tanking, and the resolution has bottomed out since it's dynamic resolution; would you not agree that CPU is likely the culprit? If the CPU is the culprit, there is still up to 30% improvement in optimization here that happened, with a much better looking game over BF4.
Where exactly do you think that 30% came from? You see, we're not interested in proving that PS4 is superior to XBO. We've known that for a very long time. We're interested in the innovation aspect. All you've been tossing up are arguments that fit your needs. Mainly, you are trying to debate PS4 is a better and more powerful system; frankly none of us care.
We're interested in the 30% gain.