Maybe you're saying the hearsay was Sony exaggerating how bad hard drives are? But they didn't really do that, and the devs would already have experience with hard drives.
If the Helldivers devs were influenced by what Sony said, they must have misinterpreted it and taken away an extremely exaggerated impression of how much on-disk duplication was being used for pre-SSD game development. But Sony did actually say quite a bit of directly relevant stuff on this particular matter when introducing the PS5.
But uh if the devs didn't realize that, I blame them. It's their job to know basics like that.
Everything else about the PS5 SSD and storage subsystem was mere icing on the cake and/or snake oil.
And on top of any potential confusion between normal SSD and fancy SSD, a mailbox is a super tiny asset and the issue in the spiderman game is very rapidly cycling city blocks in and out of memory. That's so different from helldivers level loading.
So the PS5's SSD architecture was what developers were familiar with when they tried to figure out what changes would be needed to make the game work on PC.