All i am saying, and that's not an opinion, is that if you take any game and focus on a single platform it will be better for that platform than if the game was developed for multiple platforms
That is true. I, nor anyone else, I think isn't denying it. What I am saying however is that the difference between 'focusing on a singular platform vs. a game that needs to run well on two platforms' is smaller this gen than any gen before it.
It IMO doesn't even have to do how big the [performance] difference is between consoles. What is relevant is that they are both similar in design and technology. It's a bit like having two identical consoles, one just clocked a bit higher. Both can do the same, just one can do it a little quicker. Last generation, it wasn't quite that simple. There we had two more unique hardware that did different things better. One was better at raw compute (that is well suited for physics), the other was simply really efficient and more balanced. So the best of both consoles went in different directions and those that needed to tick both boxes, had a much lower common denominator.
This time around, that 'common denominator' is much higher and therefore much closer to that 'potential maximum' anyway. So the difference between well organized good multi-plat games and exclusive impressive games is that much smaller.