GGG: we're planning to make it so that the leftmost identified weapon in your inventory will also be selectable in Crucible encounters.

From the Recently askes Questions (https://www.pathofexile.com/forum/view-thread/3324396/page/4)

Will you consider adding a Crucible specific equipment slot (like for Sanctum relics) so that players don't have to potentially sacrifice levelling gems in their weapon swap?

To address this feedback, we're planning to make it so that the leftmost identified weapon in your inventory will also be selectable in Crucible encounters.

While being somewhat of a bandaid fix, this will make the map-to-map gameplay so much smoother.