Look its quite simple.
Lets go back to the xbox 360 / PS3 era which of the consoles allowed cross platform play ?
https://www.fudzilla.com/news/gaming/21587-ps3-portal-2-has-cross-platform-play
https://arstechnica.com/gaming/2007...play-between-the-ps3-and-pcs-through-gamespy/
How many did microsoft allow in the 360 era ? As far as I know a big fat 0.
They screwed up with the xb1, they lost huge market share and all of a sudden cross platform play becomes important for them.
With PS3 multiplayer wasn't behind a paywall everything was free, xbox360 everything was behind a paywall. Sony got slaughtered in the media for the ps vita custom memory cards, but what about the custom 360 hdd port ? The ps3 and ps4 you were free to put in any off the shelf laptop hdd, even this generation f2p games are behind the xbl gold pay wall, not so with Sony ps plus, although I still wish they kept normal mp outside of the ps plus pay wall.
Sony with the ps4 did some seriously innovative stuff like game sharing a share button etc, all of this stuff microsoft is adding this gen.
Now coming to the topic at hand, there is a significant shift between how the PS5 handles the I/O and by extension the SSD and how Microsoft are handling it, rapid asset streaming should make porting new gen games to previous gen a contentious issue - Its obvious why Microsoft are making "device exclusivity" a big deal, its because they have been caught with their pants down, all they have seen and/or cared about is peak TF performance, this is what they thought would be the winner for this gen, but its not. Sony threw a curve ball which caught most of us completely off guard as most of us were thinking the same thing about higher tf numbers being king, Sony has gone entirely with efficiency all the way from SSD to GPU making sure that the GPU is handling load as efficiently as possible, not about the peak performance but sustained performance and rapid I/O.
When Sony's strategy is properly utilised and it will be straight away as the majority of it is handled autonomously using custom silicon then porting games between generations becomes difficult. The custom silicon doesn't exist in previous gen, nether do the SSDs, what is possible with their current gen hardware should not be possible with previous gen hardware. The problem is existing game engines, this is why Sony approached Epic to make sure that UE5 can properly handle what Sony can offer - its an engine used by many indie devs and AAA devs, Epic has sorted out the headaches / issues for 3rd party devs that use unreal engine to be able to switch between current gen ways of doing things and next gen hopefully seamlessly as for Sony internal engines, its something none of the devs have to worry about, Sony typically cuts support for the previous gen and encourages its internal studios to only target the latest current generation, allowing them to create games possible for the newest hardware.
What I am trying to get at is that Sony will allow Naughty Dog / Kojima / Guerrilla / Santa Monica / Japan Studios / Insomniac etc.. To make truly new experiences where they can create game worlds that literally jump between completely different worlds in a second or fractions of a second that properly utilises the I/O streaming etc.. Microsoft didn't even think about this approach, their console is very similar to the previous gen, this is what happens when your lead architect is a games developer with many years experience writing games and utilising hardware (a true games engineer) vs a sales man at the helm, I bet Phil Spencer has never once written or worked on a game.
Time will tell, but I honestly think this is just a repeat of last gen, Microsoft have been caught with their pants down yet again, have gone for numbers that on paper look good thinking this is the strategy to guarantee victory and Sony have instead gone a completely different much braver route trying to change whats possible. All of this stuff about velocity architecture / 100 G ssd being dedicated to act like RAM etc is nothing but an admittance that they got caught with their pants down, they didn't anticipate this strategy and this is why they are so heavily trying to change narrative and make it about scaling across ecosystems and any other thing they can throw around - I am so glad they are not market leaders as its obvious Microsoft have absolutely no vision, they are copy cats through and through.