1. Half-crouch, gotcha. 

2. Spider legs sticking to the ground, gotcha.

3. You stated that it takes the Archivist five seconds to reach Fuchsia. Fuchsia is by no means standing still during that, he is in fact running backwards, which means that the smoke is by no means covering more than 1/3 of the spider's approach. Following that, he is fully capable of firing a second shot at the same angle he is already holding his Hellzooka (which will hit the Archivist perfectly if he doesn't dodge) before jumping. He has plenty of opportunity to attack accurately and dodge effectively.

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Edit: 

As Skallagrim said, the Archivist is fully capable of reaching Fuchsia quickly. But I had to go by the fact that Melonhead's previous post clearly states "It would take him less than 5 seconds to reach him."