I tried explaining it to someone on VGC who eventually understood but it was still perplexing how they thought otherwise. I explained that the consoles are limited by their hardware. The performance ceiling of both is set in stone. There is nothing that will change it. A better API will simply allow developers to max the hardware faster. Not surpass hardware limitations. So even if an API came out that somehow gave the X1 a sudden advantage it wouldn't last long because it would just mean accelerating to that brick wall while the PS4 surpasses it. It's also the reason why multiplatform games will eventually have a bigger gap two years from now than they currently do. Because the games will tax X1 hardware while the PS4 will still have room to improve.
It is comprehensive that some things that the API will change the situation because they saw the PS3 having a hard time to match/catch the 360 performance in multiplatforms until the late in the gen when PS3 started to show some good multiplatform game even better than 360 version.
But the issue is different now... PS3 had a software issue... it was hard to developer, have a non-shared memory pool so devs needs to work to reach best performance and the hard coder Cell (not all devs used its SPUs)... so PS3 had a issue that you can work hard to improve it... Xbox One have a physical issue here that even working hard won't change because it is physical.
I will give a example with Tennis (table tennis to be fair)...
My brother was really good at table tennis but he broke his arm and can't play for some months with his right hand (his best)... so he started to play with the left hand (the bad one) until became good and even surpass the right hand... the funny thing is that today he is better with the left one than the right one and he can play fine with both... this is the PS3 case.
Now for Xbox One think if my brother had lost the some movements of the left hand... he could worked hard, train a lot, play a lot and because some physical limitation he will never make the left hand play like the right one because in this case the left hand is physically limited compared with the right one... in my previous example (real life example) the left hand was just hard (more time and work) to became better than the right hand... no physical limitation... it was just more hard to work/train the left than the right.