Yes and no. All of their systems were past peak sales upon being replaced:

Granted, the PS2 was still doing decently when the PS3 came out, but it was replaced four years after its peak. The PS1 was replaced sooner after its peak, and it was still doing well when the PS2 was announced, but then again it was starting to slow down. Sony might have been able to hold off on the PS2 for another year. Meanwhile, the PS3 was starting to decline fast after 2011. It (and the 360 as well) had a belated peak compared to historical norms, but that also meant that by time it passed its peak, it had already reached the majority of its potential audience, and Sony was rapidly running out of new customers. As for the PS4, it's still doing well and arguably hasn't quite passed its peak yet. Unless Sony refuses to issue another permanent price cut, the PS4 might not start to enter a clear terminal decline until next year.

Also, it's worth pointing out that the PS1 & PS2 existed at a time when the tech was progressing at a proportionally much higher rate. I believe last generation was as long as it was on purpose because of the rate of technological slowdown. Imagine if the PS4 had come out in 2011 instead of 2013. It'd be either much weaker, or much more expensive. I think it behooves Sony (and MS) to wait a bit longer and not rush the transition to next-gen. The upgrade needs to be worth it. While the PS4 might be officially entering the last phase of its life, I don't think that means that the PS5 is imminent. I simply don't see it coming out any earlier than 2020.

Two issues that go hand in hand. Five years used to be more than enough to give us a massive leap in technology. We went from the SNES in 1991 to the N64 in 1996. The GameCube's GPU was rated at least 47 times more powerful than the N64's. The PS3 was a comparably large increase over the PS2. Meanwhile, the PS4 & XBO weren't even a full order of magnitude more powerful than the PS3 & 360 despite a seven year gap. Honestly, the PS4 Pro and Xbox One X are how powerful the PS4 & XBO should have been at launch, but couldn't because they'd be prohibitively expensive in 2013. That was a ten-year gap between the PS3 and the PS4 Pro.

It's taking longer to get the kind of power increases we used to see in previous generations. And then there's the diminishing returns. While there's still a ton of advancement that can be done with game graphics, the leap from the 360 to X1X doesn't yield the same qualitative increase in graphics that we saw in the jump from the PS2 & Xbox to the PS3 & 360, which in turn wasn't quite the jump we saw from the PS1 & N64 to the PS2 & GameCube. It takes a significant quantitative increase in specs to yield a quantitative increase sufficient to justify the upgrade to a new generation. This is especially the case today with the push for 4K and and 60 fps as standards, as those things come at a price. If we stuck with 1080p30 as the standard, we'd see better graphical results.

The slowdown in tech advancement combined with diminishing returns is why last generation was so long. And that's why this generation needs to be at least as long. The PS4 & XBO still have the potential to generate steady sales well into 2019. We've seen YoY growth for the XBO thanks to the cut to $230, and, especially given how well the PS4 did in November, Sony could also generate significant growth for it as well by cutting the PS4 to at least $250. I don't want to see next-gen rushed, and I absolutely do not mind waiting until 2021 for next-gen consoles. I also wouldn't mind paying $500 at launch, either. Assuming 2% annual inflation, by Nov. 2021 the PS4's inflation adjusted launch price will be upwards of $460, and it was pretty damn reasonable price at the time (on par with the PS2 & Xbox, not too far ahead of the SNES & Genesis). I think the market will be ready for a $500 launch price by 2021, especially if the technological leap is worth it.

Considering the MP of all those games is tied to a PS+ subscription paid to them (Sony), I don't think they would made such a deal out of it. 

That's always a bulk process, not a HPP (High Power Plus) process as needed for PCs, Consoles and servers. Bulk processes are ready earlier because they are less complex but in return also much less powerful. For High Power processes server chips or High-End GPU are generally the way to go. Hence why the x86 and GPU production at TSMC is coming later: Their High Power Process is not yet in production, only their Bulk processes.

Edit: The problem with not building monolithic is small with CPU (mainly just higher latency), but not nearly so easy to solve in GPU. Navi is potentially (and hopefully) coming with a solution to this problem, otherwise it will need a pretty big GPU - bigger in square mm than PS4 Pro by around 50% even though produced in a 7nm process just to get a chip powerful enough to get enough distance between itself and the Pro. This would not only be pretty expensive for a console chip due to it's size, but also a pretty large heat producer

Two issues that go hand in hand. Five years used to be more than enough to give us a massive leap in technology. We went from the SNES in 1991 to the N64 in 1996. The GameCube's GPU was rated at least 47 times more powerful than the N64's. The PS3 was a comparably large increase over the PS2. Meanwhile, the PS4 & XBO weren't even a full order of magnitude more powerful than the PS3 & 360 despite a seven year gap. Honestly, the PS4 Pro and Xbox One X are how powerful the PS4 & XBO should have been at launch, but couldn't because they'd be prohibitively expensive in 2013. That was a ten-year gap between the PS3 and the PS4 Pro.

It's taking longer to get the kind of power increases we used to see in previous generations. And then there's the diminishing returns. While there's still a ton of advancement that can be done with game graphics, the leap from the 360 to X1X doesn't yield the same qualitative increase in graphics that we saw in the jump from the PS2 & Xbox to the PS3 & 360, which in turn wasn't quite the jump we saw from the PS1 & N64 to the PS2 & GameCube. It takes a significant quantitative increase in specs to yield a quantitative increase sufficient to justify the upgrade to a new generation. This is especially the case today with the push for 4K and and 60 fps as standards, as those things come at a price. If we stuck with 1080p30 as the standard, we'd see better graphical results.

The slowdown in tech advancement combined with diminishing returns is why last generation was so long. And that's why this generation needs to be at least as long. The PS4 & XBO still have the potential to generate steady sales well into 2019. We've seen YoY growth for the XBO thanks to the cut to $230, and, especially given how well the PS4 did in November, Sony could also generate significant growth for it as well by cutting the PS4 to at least $250. I don't want to see next-gen rushed, and I absolutely do not mind waiting until 2021 for next-gen consoles. I also wouldn't mind paying $500 at launch, either. Assuming 2% annual inflation, by Nov. 2021 the PS4's inflation adjusted launch price will be upwards of $460, and it was pretty damn reasonable price at the time (on par with the PS2 & Xbox, not too far ahead of the SNES & Genesis). I think the market will be ready for a $500 launch price by 2021, especially if the technological leap is worth it.