Red, in the second case I suspect the pilot would have their hands full just trying to stay in the air, gusts or no. In the third case the aircraft would have lost it and crashed long before a gust had a chance to catch it off guard. The instability you describe would affect the aircraft all the time. Only the first example and near cases of the second example will fly without an augmentation computer on board.

But you're right. Reactions to gusts are the only times an AIRBORNE plane sees any sort of sidewind. But your reaction description misses one point. The plane will yaw in response to the "new" wind direction and as well it will accellerate until it is again in a balanced wind head on mode. When it flys out of the gust it treats the previous "steady state" as a NEW wind gust from the opposite direction. The actual yawing and any sideways acceleration ensures that it becomes one with whatever the momentary wind is doing in short order. It'll always work to restore it's balance and trimmed flying state in whatever air it is currently flying within.