Let's throw in some context, what's the primary thing storage affects? Loading times. And loading is generally thought of getting stuff from storage onto RAM.
So let's take an example. I loaded up Cyberpunk 2077 and it's floating around 4GB of RAM being used. If this was from a PCIe 3.0 SSD, it'd take about 1 second to load this. If this were a PCIe 4.0 SSD, 0.5 seconds. Is that half second really going to matter in the scheme of things? To make things worse, a lot of that RAM usage isn't actually loaded from storage, it's the game's data that it generated for various things like random NPCs or whatnot. So the data that's loaded for Cyberpunk 2077 is much less, reducing the loading time even more.
And then, the kicker: your CPU is still responsible for "loading", because it still has to initialize the game, create all those data objects, among other things. Storage activity doesn't account for even most of the time loading is going on. If we went with Cyberpunk again, it took about 4-5 seconds to load. At most only a second of that would've been from storage if everything in RAM was from it (which it isn't). So in reality, almost all of the time spent loading was from the CPU getting the game up and running.