Sooo, I looked up how long Namek ran in the manga.
From Chapter 242 (the survivors learn about Namek) to Chapter 329 (Porunga brings almost everyone back to life and Mecha-Freeza arrives on Earth).
That's less than 100 chapters. I guess the fatigue comes from the anime having episodes where nothing happens.
Buu Arc is the longest arc in the manga, its about 99 chapters.
If you don't separate the Saiyan and Namek material, then they make up the longest story arc together, in both the manga and anime.
Red Ribbon Army isn't even that long compared to them, even if you factor in the Baba Tournament in it.