This isn't a convincing argument at all, I could just as easily say "any trained sushi chef knows how to cook rice properly, all they need is Amazon and access to a good rice cooker like Zojirushi".
For what it's worth, I don't believe the idea that rice is the main focus -- it just sounds like the sushi chefs are fucking with people when they say something like that.
a) it was born a few hundred years ago (Edo period) as a take-away food / fast food
b) some forms of it have become a high craft or even art that you can spend a lot of money on (compare to high status Pizzerias in Napoli)
Now whether that's legitimate or not is of course up for discussion - in my opinion it's a legitimate and fulfilling experience that you can have by going to a Sushi master if you can appreciate this kind of craft.
>It is a common Japanese legend that the truly great itamae-san ("san" is an honorific suffix) should be able to create nigirizushi in which all of the rice grains face the same direction.
While that's definitely an exaggeration, it gives you an idea of the importance of rice in Japanese sushi. Basically, it's taking something that's naturally chaotic (like cooked rice grains that just stick together in whatever fashion), and bring their entropy down to become something ordered by using the most efficient motions possible. For that purpose they use hand fans and wood to control the moisture as well as very finely trained hand motions to control the shape of the nigiri as well as the alignments of the grains.
All of that, just so the guest can pick it up with his/her chopsticks, and have it effortlessly fall apart in the mouth, in an explosion of flavour, like a two stage guided cluster bomb targeting your taste buds ;-).
So, yes, you could probably just use an automatic cooker for the cooking process (although the masters sneeze at that of course, but it sure is standard in Japan nowadays up to a certain price level) - but cooking is the easy part, the fun starts after that.