Not storage, I/O. The sheer bandwidth to get data from disc into RAM and VRAM so the CPU and GPU can use it. Games like GTA V and the Witcher (and most dense open world games) take a long initial time to load and limit the speed with which you can move through the environment.
GTA V and Witcher 3 take no longer than 20 seconds at most on my half assed SSD, so I don't really see where this long time comes from.
You can move through GTA's world at high speed - at higher altitudes. Try doing it at ground level in Los Santos and expect your experience to similar to watching a Power Point of GTA V screen shots.
I fly with jets over street levels all the time, the experience is solid even on a regular HDD, and I am not the only one.
ArmA 3 is probably the heaviest game in flight mode, as you fly over an island with an area of hundreds of kilometers, packed with details, jungles, terrain and houses that you can visit in first person, and with a draw distance extending to tens of kilometers, you fly (low pass) over all of that in the jet just fine on an HDD.
I/O. The sheer bandwidth to get data from disc into RAM and VRAM so the CPU and GPU can use it
It remains to be seen how much an advantage console IO hold over PC, and whether that will amount to any significant difference. The I/O structure on PC doesn't prevent it from offering a solid gaming experience even on HDDs, nor does it prevent from doing very low latency access on NVMes or SSDs, or having crazy sequential speeds.
For now, the biggest gain on consoles will come from storage access speeds, anything else is still up in the air.
if you set a baseline so high that everyone has to upgrade everything the likelihood is that for most casuals, they won’t. They’ve had a good run on old parts for over a decade without needing to upgrade. So either they put out the huge bucks or they don’t get to play. And if they want to play and not put out the money; consoles will easily be the cheapest method to obtain it.
PC gamers have had enough slack time, most people didn't upgrade their 2nd or 3rd gen i7/i5 CPUs, they've had those for 6 years or even more (I am one of them), they probably only had to upgrade RAM just by adding a stick or more, many people are still on their Maxwell and Kepler GPUs (960, 970, 750Ti are the among the most popular cards on Steam), most of those with modern GPUs are still using Pascal (1060, 1050, 1070), which got released 3.5 years ago, we still have another year before next consoles come out, which means all of these people will add another year to their old hardware.
So believe me when I say, most PC gamers are gearing up for an upgrade anyway, their PCs have became long in the tooth anyway, they are just waiting for the right justification and the right mix of games and powerful hardware.