I think there's a small typo there, 9 bar would be more regular for espresso.
I agree otherwise. I treat moka or aeropress coffee as its own thing; it's not espresso and that's OK.
I see a lot of people talk about "grind" as important.
Really it's just a way of varying pressure and to keep it roughly in that 9 bar zone.
The only magic in a good bur grinder is its consistency. You can look at what you're getting out and bump the pressure up or down slightly compared to your last shot.
So as the beans dry out with age, you can increase the extraction so you don't get a flat, sour shot with no crema. If you put in a new bag of beans you can make the grind courser so that pressure is reduced and you` don't over extract.
I love a morning espresso but I'm less keen on all the connoisseurship around it.