Posts like this (for some reason its always complaining about Nami Ult instead of the hundreds of other projectiles in the game) just come off as a lack of mechanical understanding.
A 'projectile' is generally any particle that travels from point A to point B with any sort of travel time or velocity. Hence, Nami's Ultimate is a projectile.
For one, the tsunami could not even be coded as a projectile.
Yes, it should. That's how the coding of this game works. What do you want it coded as? It is a projectile. Now, you could instead argue, "I think the wave should be split up and coded as 5 different projectiles, all moving in the same direction/speed together so that they visually still remain one wave. However if a 'slice' of the wall is blocked by Yasuo or Braum the remaining pieces will continue."
I still don't think that'd happen though, because once you start saying "Change X Champion's abilities so that I can circumvent Yasuo's kit" I think you get into dangerous territory. However, the argument itself would be reasonable. Rather than just "This ability should go through Yasuo's wall because I said so."