This isn't just a matter of reducing load times.  Designing games around an SSD can actually make fundamental changes in level design.  Most games today aren't just loading once.  They are constantly streaming in huge amounts of assets. 

Mark Cerny used the example of Jak II on the PS2.  Jak II had to use tricks to hide load times, but it also used tricks to manage streaming in the world.  

The pathways in the world were made so that the game could stream in the next area's assets.  

Current gen games are doing a lot more of this utilizing the hard drive.  But we are still working with the same kind of limitations. 

Current games have to utilize tricks like lowering quality of textures, making less dense worlds, etc.  

A small read by a former Naughty Dog dev:

PC has had access to SSD for something like 10 years. I'm sure a lot of PC games are already capable of taking advantage of you having an M.2 drive. But this high speed SSD being in PS5 will pretty much standardize taking advantage of faster SSD for all games on PS5 and PC. So it should be exciting times.

I'm kind of afraid of the HD trying to make up for limited RAM like it did last gen. That tends to make consoles age poorly. If RAM requirements of PC games balloon into 32 GB, the shared VRAM and RAM of PS5 will not be enough. Series X would be even worse off. Then they'd leverage the SSD speed in PS5. But overall that would make both Series X and PS5 age terribly. Unlikely scenario, but just a thought.

One thing about the "PC have SSD for over a decade" that I want to ask, can it load most current gen games in 1 or 2 seconds?

The first SSDs? No. 

Not that.

Because from what I see SSD can cut the loading by 60-80% compared to HDD. But that would make a 1min game taking 10s to load, so PS5 solution would still be a lot faster.

Ok so it handles texture pop in, or in this case near eliminates it. On top of loading times. Good to know, but most gamers will be comparing resolution and FPS like always.

DP 

The only PC game right now that is taking advantage of the SSD somewhat similar to next gen consoles is Star Citizen.

It's not just a matter of texture pop in, but actual level pop in. Devs have fewer restraints for level design.  

And this is about how it benefits both consoles.  

No, I've explained it in two other threads.

The reason why you only see marginal impreovement is the inability of pcs/current consoles to do what the PS5 hardware can do "behind the controller". No pc in the world can achieve this, no matter how fast the ssd is, because the hardware simply isn't there. Detours are required, particularly in pc who simply can't directly stream into gpu memory space. At uncompressed 8-9GBytes/s, loading an entire game/continuing a saved game should take less than 2 seconds on the PS5.