I wouldn't actually have wanted him to rush in now, possibly ruining what Erwin and Levi had in mind, but I'd have liked him to want to rush in. That's the difference. He wouldn't need to be an idiot who ruins everything, but he could be a man who would eagerly use every opportunity to kill a titan and get stronger by doing so. A main character with no initiative of his own is annoying.
I wonder which parts of these episodes made you think anybody but Erwin and Levi knew that beforehand. Because it sure looked to me like even the brainman, Armin, realised it only when they were already in the forest.