That be me adding to the confusion, the times I've investigated the free space required to install a patch on my PS4/PS5 it's always been in-line with the full game size, I wasn't aware it could be less as I've never seen it.
That seems to be the crux of the topic, and why I suspect it had nothing to do with fragmentation at all (or if it was, despite my reservation on its usefulness given you'd want all the games files in linear order which this wouldn't maintain, it was at least a secondary action). Because there's no journaling you still need to ensure data integrity, hence the patching method which is still there even on the SSD.
Xbox's patching seems to be random to me (seems to be based on the age of the xvd and the manifest rules used to build it?), but Nintendo's patching is different again from both of them, because of how the carts have to work. You simply download a kind of xdelta patch that's applied to the master ROM at run time. An update simply replaces that patch with the latest.
