Nah, we're going to be getting something that has at least 2x the performance of the X's GPU.  Sony is going to want to be able to wow people with it being 2x+ more power than the X, which is supposed to be a beast.  And like you said, there is going to be a big difference between the Zen core CPU and the Jaguar cores found in the PS4/XBO.  Should see, at a minimum, 16 GB of GDDR6(X) RAM, maybe with 1-2 GB of DDR4 for the OS.  Sony's going to make sure they squeeze as much out of that $399 as possible.  Launching like they always do, taking a slight loss, but making up for it in game sales.

You could ask yourself that same question for any of their consoles, really.  The answer is, they aren't cutting their sales short.  They are making sure the PS momentum continues.  As soon as interest starts to wane in the old console, then BAM! here's the new one.  Not only do the new systems sell well, but the old ones continue to sell well, too.  The PS1 still sold ~30M after the PS2 launched.  The PS2 sold 50M+ after the PS3 launched.  Again, the only outlier was the PS3. 

The reasons it didn't sell so well after the PS4 launched are many fold.  First, it wasn't quite the force the other PS systems were (which the PS4 is, again.)  Second, they weren't able to drop the price to $199 until after the PS4 launched, while the PS1 was $99 and the PS2 $129 when their successors were launched (the PS4 should at least be able to get down to $149.)  And third, the PS3 had an extended time on the market before the PS4 launched. If you the PS4 launched in 2012, and sales for the PS3 stayed similar, it would have done ~20M after the PS4 launched, as opposed to ~8M (I think Sony is going back to the model that worked best for them, a 6 year gen length.)

The fact is the people waiting to buy a PS4 at ~$149 are not the same people willing to buy a PS5 at $399.  I could see the PS4 easily hitting 20M+ after the PS5 launches, even if its in late 2019.

I believe Sony needs to fix the launch date before designing the components for their PS5. They can't build a system on components coming out in 2021 and then release the system in 2020 after a sudden drop in PS4. or build a system on components of 2018 and then delay it by a year or two if they find PS4 doing pretty well. 

Definitely they have some flexibility in extending the design by lot of things get built around the specification of the hardware like compilers, IDEs, debugging units, game engines. So we can all argue on when Sony will be launching the PS5 but i m quite certain that Sony by now must have finalized the release year and components of the system. 

I make bad bad comments about each if I think they deserve it.

A 2018 ps5 at 399 would be about equivalent to the X. So a 2019 ps5 at 399 would only really have about 1 year of advancement. I think you overestimate the rate in which tech is advancing/coming down in price. I don't think ur putting in a 12tf gpu, with a good processor, and new expensive ram, then cooling all that tech inside a small box for 399 in 2019. To me what ur describing is either a 2019/2020 console at 499 or a 2020/ early 2021 console at 399.

I think you underestimate it.  Including how fast prices drop for components.  By the end of 2019, it will be quite easy to build something 2x the X, while taking a small loss on a $399 price.  Especially, when you consider the discount Sony gets on ordering mass parts.  And even more so when they can use the sales of the PS4 to barter for even better prices.  Something MS can't do.

You have any source saying it's 1.3m?

https://www.resetera.com/posts/2141920/

https://www.resetera.com/posts/2141920/

So It was basically between 1.3 and 1.5 million. So u decide to go around saying it's only at 1.3 million. And you state it like it's a matter of fact.