Thank you for the translation! I really like this series. It gives a different perspective on a hobby I really like.
Personally, I am a staunch advocate for brush painting. It's way more fun than using an airbrush, it teaches you a lot of important skills and it helps you improve/practice your fine motor skills. Then again, I paint models for war games and tabletop role-playing games. It's probably different for gunpla!
Indeed it is! Gunpla, as well as just about all other scale models, often require broad areas to be covered in a single color, a task airbrushes can accomplish easily and quickly.
In addition, the thin coats left by an airbrush allow for pre- and post-shading and gradients.
Furthermore, because of the evenness and smoothness of the layers, airbrushes are great at painting metallics and almost indispensable for candy coats.
That said, one is always welcome to use any techniques they want. I have an acquaintance who is hand-painting a Master Grade Aegis Gundam with Games Workshop colors. He's going with a color scheme inspired by the Infinite Justice Gundam's Real-type Color variant, the parts look incredible so far, and I can't wait to see the completed kit!