Thing is, we don't know that that's true either. There is no way Sony engineered their SSD the way they did without a damn good reason. It clearly took up a decent portion of the cost of the system that could have been allocated to silicon for the GPU/CPU. So we know Sony made those choices/tradeoffs for a reason. I'm sure they worked closely with Epic on the tech, they even said as much when the demo was revealed. You're conflating financial investments with bad faith statements out of assumption. It's certainly possible that's the case but the bottom line is none of us really know. Epic is on record as saying the demo at that level was only possible through the PS5 SSD speed for reasons of how the technology works and loads assets directly into RAM on a per frame basis, or something akin to that. If it turns out in a year or two that they can do the same or better on the Xbox Series X then we will know it was a straight up lie. If the tech bears out their statements in the future, then they didn't. Unfortunately it's going to be a decent wait.
We all know Sony put a great deal of focus on their SSD I/O solution, but my issue in this constantly being mentioned is that some folks who do it, do such with the accompanying baggage of downplaying Microsoft's solution or comparing them apples-for-apples while ignoring the specific (and intentional) differences in their approaches for leverage by adjacent technology divisions in their respective companies. I think that sets up a bad narrative and the fact there's Sweeney out here on Twitter acting as though the XSX doesn't even exist when it comes to next-gen storage I/O solutions kind of does (through no fault of his own) feed a reaffirmation to some fans who unfortunately do utilize that in bad faith arguments regarding the next-gen platforms.
So this news coming to light about the investment of $250 million by Sony, at least that clears the air a bit on a very strong motivating factor that most likely (assuming Occam's Razor theory) be at some root to Sweeney's statements the past month or two. And some of his statements, like saying the UE5 demo would only be possible on PS5, well now we can see they have a lot of PR fluff built into them even if in some ways they are technically true.
I actually crunched through some numbers to arrive at this conclusion. For that flying segment, let's say they are streaming in 8K texture assets raw/uncompressed with a new texture asset per frame. A raw 8K texture is approximately 99.5328 MB. At 30 FPS, that is 2.985 GB/s. Which, clearly, is larger than XSX's raw SSD bandwidth (2.4 GB/s)...but this is where the tech demo part comes into play.
How much genuine game logic is running in that flying segment? Virtually none. There are no enemies, probably not much in the way of physics, no game mechanics at play etc. Since on PS5 the dedicated processor in the I/O block has DMA to the system RAM, that also means when it is transferring data from storage to RAM (or vice-versa), the CPU and GPU have to wait. That's a tradeoff in a hUMA architecture design (it's also a reason the I/O block has the cache coherency engines and is using a smaller SRAM cache instead of larger DRAM cache (speed/latency)). But in what real gameplay scenario do you expect the system to spend an entire 30 consecutive frames simply streaming in 8K texture data from storage to RAM to then get crunched by the GPU? It's not going to happen!
Now with that example just above, the PS5 would actually be streaming in each of those 8K texture assets raw well efore it's SSD actually hits its bandwidth limit, which is why in that scenario you'd still be able to have the GPU work with the texture data in RAM even if it's being quickly streamed in, it'd just be the I/O block and GPU alternating access along the memory bus. But that's even assuming the flying section in the UE5 demo was streaming in unique 8K raw textures EVERY FRAME, which is very likely wasn't. Remember the statue room section? Each of those statues used the same texture and poly model, but that doesn't mean you need the SSD to stream in duplicate texture and poly model data for each statue; you just stream it in once and have it sit in RAM, the GPU is doing the brunt rendering work there (just like in any other case involving visual calculations and output to the screen).
Assuming XvA has most of the features of PS5's SSD I/O (and at least all of the key features; already discussed that cache coherency engines are not necessarily "key" features since those are more due to a requirement specifically of Sony's design to ensure it works properly), for recreating that flying segment in an actual gameplay scenario, it should have no problem doing it at the visual fidelity of PS5 considering there are other things XSX can leverage to make up for specific parts of the pipeline, via GPU ML texture upscaling. More importantly though is that one thing MS have consistently mentioned regarding XvA is high granularity in specifically choosing ONLY the texture asset actually required; Sony's solution is obviously faster in sheer numbers but in this specific area seems to have less a focus on granular/selective load targeting of specific texture data (or portions of texture data) to stream to memory, it favors a different approach good in its own way however.
Investing $250 Million into a company has to come with some benefit, am I right? LOL I don't think that's farfetched at all. The extra step in claiming it was specifically a marketing deal, a secret one at that, is a little farfetched to me. The claim that EPIC was holding on showing the demo on Series X doesn't make dollars and sense to me.
Yeah, I think it's the perspective into it from this context where the merit comes into play. It's a bit ridiculous to say Sony paid Epic money for the demo on PS5, as you say. Especially seeing they have held demos in the past on Sony consoles as far back as PS2.
But this investment from Sony into Epic likely was at least in talks well before the demo came out, and the PR Sweeney's done for the platform post its release is certainly a good perk due to it, even if he is touching on some elements of truth to a decent extent.