Light is not a molecule, but is behaves as one. Light behaves the same as any particle, following all the same laws. In the same way light can travel and physically interacts with the world around it. As such light is highly comparable to a molecule, as in no way does it change the math applied to a molecule when you apply it to light.
Just as a molecule does, light travels, and is a projectile. A projectile does not need to have mass to be a projectile. That is just flawed logic. Anyone who works in programming could tell you that everything we work with, from physical objects to light, does not require reprogramming how the laws of nature function to make a particle behave normally at a mass of 0. It does not interfere with any of the laws of nature that we are making a program abide by. I can throw a 10ft cube in a simulated world that functions as ours does and give it a mass of 0. It works exactly as it theoretically would in real life, aka the same way light does. It can be a projectile like any other.
This isn't us twisting the laws of physics to suit a video game, this is simply how the laws of physics apply. That 10 ft cube is most certainly a projectile so long as it is moving, and it has a body. It not having mass does not change that in any way.
Your logic is flawed because a projectile is not defined as having mass, it is defined as having a body, and a body can exist with a mass of 0.
Either way this isn't something that can be discussed properly as you are trying to force real life logic on a video game. At that point you have to apply rules of the game as though they were real life. It doesn't just stop at Yasuo windwall blocking all projectiles. You then have to realize that the game's definition of projectiles is different than yours. Then everything that is defined as a projectile changes. Suddenly you get to the point where putting game logic in real life completely erases real life with game logic. This is because the game exists in real life, so the logic in the game is not flawed, as it is a reality within a reality, and according to the logic of our current world, Viktor laser is blocked by Yasuo windwall because if, in real life, I shoot a viktor laser at a yasuo windwall it gets blocked. Why? Because I am playing LoL and that is how LoL works... In real life.