I think you're missing the point made above: the paper compares apples to apples (broccoli with and without shade) for good reason, but the ability to cool the microclimate may enable crop substitution that has better output/value in areas where it is normally too hot for that crop.

This isn't something that's particularly obvious unless its pointed out, poly tunnels work on two fronts:

1) extend the growing season/climate control

2) scatter direct light into bright ambient light meaning that plants aren't scorched.

"leafy" plants like pumpkins, tomatoes, cucumbers etc "wilt" when in direct sun. they go floppy to stop evaporation. THis means they don't grow as fast. If you even out that light so its not directly heating the living shit out of the leaves, they grow faster, because they have less time in stress.