Yes they are but they also has to take in considerations. A Last of US 2 for example does look like that because they have the same tech on all platforms.
Developing games with a SSD or HDD in mind for example would be a bigger gab then a Sony and Switch game for example. Having a SSD as base will revolutionize games. They can be much more dense, they can be much bigger full of life and objects. The methods of streaming game worlds will be a totally different view.
So if one console does not go for a SSD as well we will not see has much evolution and change as people want for a new generation. And I think that is really sad. Imagine how a GTA would be able to look with just a SSD in Mind. Your brain would explode.
Don't worry, SSD as the base for games is coming, it's just not quite time yet. If you're a multiplatform developer as MS is, there's going to be a transition period.
There might be some wiggle room for improvements on PS4 / X1 with external flash storage in the mean time, but requiring that would fragment your userbase and might not ever be worth it.
I TOTALLY forgot about that new MS initiative (that every 1st party game will run on a PC). You're right about that. MS really is literally all over the place.
MS have been working towards this for years, and delivering on it for about two. At the moment you need to support down to about a moderate quad core from a few years back, and a mechanical drive, and be able to hit around 60 fps (GPU permitting).
In light of that, I don't think supporting the X1 is going to be
too much of a drag if you're happy to just go for 30 fps. But the further past 2020 we go the more that will change, of course.
The market has hit an inflection point in terms of increasing core counts and the cost of flash storage is continuing to drop. Dropping PS4 / X1 for AAA games is inevitable, it's just not going to happen on PS5 / Scarlett launch day.
(Might do for some PS5 exclusives, of course, because Sony don't support the PC or have a Gamepass like service, and it might be worth creating exclusives even if the games
could conceivably scale back to PS4.)