No idea why you put that video there.
It has almost nothing to do with what I said...
I didn't say the graphics of the rain were terrible, or that it wasn't difficult to drive in the rain in reality. What I said was they've got the level of difficulty way wrong with full wets... When it's raining medium (to where you still need full wets, but not Japan GP 07 kind of rain) full wets will not be sliding around like they're driving on Ice... that's consistent across any sport, even when they don't have traction on!
The full wets in the rain on GT Sport, drive like you'd expect slicks to, with absolutely zero grip... which just makes zero sense at all.
It provides a comparison for how it is for him to drive it in the wet. You can see his inputs, so you can see, for example, to what extent he's having to use partial throttle, you can see his lap times to compare against dry lap times, you can see times when it squirms about because he's used more throttle than ideal at that point in time. You can generally assess the relationship between his inputs and the car's behaviour, in real life, in the wet, which seems pretty relevant to me.
GTS daily race Gr.3 Monza RM dry world #1 1:45.8. His best time in the wet 2:02.06, difference 16.26 seconds. It would be nice to know what he would have done in the dry in the same car, of course, so feel free to provide additional relevant information if you can find it.
GTS daily race Gr.3 RBR RM dry world #1 1:27.375. Manufacturers free practice full wets world #1 1:44.093, difference 16.718 seconds.
Obviously this can only be seen as a ballpark comparison for several reasons, but as far as it goes, the change in lap time in GTS seems reasonably in line with his best wet Monza lap time.
In terms of subjectively assessing the difficulty he is experiencing, based on the relationships between his inputs and the car's behaviour, I'm not seeing a huge night and day difference compared to what it looks like when you watch a top 10 replay from the manufacturers leaderboard. Also, he says that they had maxed out the rear downforce to give more rear end grip in the wet, which we can't do for manufacturers.
As another test, I just created a lobby where I could try out a car I've owned, the Civic Type R, in the wet. In real life I know this has plenty of grip in the wet with standard road tyres, it's not at all difficult to drive in the wet. In GTS, it was also very easy to drive around RBR in the wet on Comfort Soft tyres. I tried Wet tyres, and they were also fine. I didn't do enough laps with each to see the relative lap times, but when I turned the wheel left and right on the straights to feel the level of grip, the wets felt more grippy, which I think is what we'd expect?
This should probably all be moved into a thread on wet physics in GTS.