Under which condition is a forward CG most critical?
One intuitive way to think about this is that the pitching motion of a rigid body occurs at its CG. At forward CG, the elevator, which pitches the aircraft up, indeed has a longer moment arm. On the other hand, however, the wing lift vector, which tends to pitch the aircraft down, also has a longer moment arm. The proportion of change of the wing lift moment arm is quite a bit more than that of the elevator, for the same change in CG. In the end, the wing lift, which is also quite a bit larger, wins this race. Hence, forward CG is more critical for maneuvering.

Strange that it says landing, which I assume is the flare portion, is the most critical condition. I would've thought takeoff rotation would be equally bad, especially if you have a mistrim.