I’m speculating using a physical hard drive will be a poorer user experience - ie: being slow to stream the world data causing pop in, texture loading issues etc

Wouldn’t that need Windows 11?

Possibly, but not necessarily.

Many video games contain multiple versions of assets to place them near each other when a new level gets loaded. This wastes a lot of space, but it makes loading the game on hard drives a lot quicker. With SSDs, you don’t need those multiple copies. In fact, fragmented files are theoretically faster than linear loads. You can just pack the assets once and load them in when necessary, even if the assets go through RAM first. However, hard drives will suffer significantly in their load times and possibly pop-in or video/audio stutters.

Loading from SSD is also fast enough that it’s possible to use less intensive compression for the same loading speed. On hard drives compression can quickly benefit loading time as the CPU is faster at decompressing content than the hard drive can serve raw files. On SSDs, less densely compressed files should cause fewer CPU overhead provided there’s enough RAM bandwidth available.

It’s also possible that hard drive optimisations were just deemed not to be worth the effort with modern gaming systems. With SSD prices what they are, I would certainly appreciate it as a developer if my boss would tell me not to bother with testing and optimising one specific slow configuration.