Your comparison does not account for staggered launches which obviously puts the PS4 at an advantage. Aligning the launches by region puts the PS2 ahead of the PS4 by about 10m and that margin is only going to grow in the PS2's favor because it had higher peak years than the PS4 is going to have.
Xbox One is not doing fine. If it was, then Microsoft would have not decided to hide its numbers.
No idea how you've come to the conclusion that the console market is the healthiest it's ever been when four of the five eighth generation systems have seen significant declines over their respective predecessors while the one system that is going to beat its predecessor will only do so by a rather small margin. The state of the eighth generation is lackluster which is why all console manufacturers have opted to come up with ways to increase revenue per customer. One of these methods is to put out more hardware revisions to make people double-dip on hardware and make the hardware numbers look better than they really are.
The PS4 has already one model more than the PS2 had, but it's not going to stop there. Sony will put out at least one more revision because they don't have a choice in light of the sales they are getting. And mind you, the PS4 is the most successful system out of the sad bunch in the eighth generation. It's going to need more than the three models it has had so far in order to cross the 100m mark, and Sony will release at least one more revision.
ok, answe this simple question..... why did they have staggered launches back in the day?
If you truly understand why, then you would know why its not an unfair way to make a comparison.