What you say is true, but this gen there is one thing that changed: until 8th gen even base models had a huge RAM size increase compared to previous gen.
But this gen full specced models offer a big, not huge increase, and XS base model offers an increase quite small, smaller than the typical mid-life RAM upgrade anyone would do to their PC. And PC-console multiplats are more than in the past, and since PC gaming dropped DOS, with PC development comes the developers attitude to put less work than in the past on RAM usage optimisation.
The amount of RAM is less crucial on 9th gen consoles due to the SSDs being able to accommodate a lot of the stuff that used to be done in RAM on older hardware, and since XSS has the same SSD as the X, it still shouldn't really hold back the X or PS5, especially when things like textures and resolution can be easily lowered to save memory.
Don't believe SSD is a replacement for RAM, SSD is great because it's a great speed and latency improvement compared to HDD. Yes, precisely thanks to these features an advantage offered by SSD is being able to load in RAM a lot of stuff "last minute" as smoothly or even more than loading larger portions in advance from HDD, so keeping a lot more RAM available on average, but when you need the speed and latency of RAM, SSD won't be a replacement.
Also, in single player games with free roaming in large worlds managed in real time also outside of draw distance, the game engine will need to keep loaded all the non graphic world infos needed for the task (well, for this particular issue we're talking about a very small minority of very ambitious titles, but even if they are in small number, surely both Sony and MS will want them on their latest consoles).
I took into accont graphics scalability, but I'm also willing to take into account that even the entry level GPU is more powerful, and some years newer, so it offers more and more advanced functions, even limiting it to 1080p it will still require more RAM than last gen, I fear 10GB is just a couple of GB too stingy, 12GB would have made devs life easier. BTW 12GB was precisely one of the most agreed upon guesses about entry level RAM size before PS5 and XS were fully revealed.
Anyway, I don't predict doom and gloom, I just predict that eventually the compromises required by entry level XS will force devs to not fully use XSX, and PS too in multiplats, CPU power and their larger RAM will mostly be used only for better graphics.
Anyhow, it could also happen that XSS limits become a good excuse for devs to pause the race to ever more demanding games and prevent dev costs from skyrocketing.
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