Where did this idea come from, and why is it so prevalent? You can cover an entire map in electro flares, leaving a puddle of shadow for your troops to hide in. The entire mission becomes a breezy-easy shooting gallery, with all the enemies illuminated for the brief seconds they exist before they're torn apart by reaction fire. Night missions are easier and faster than day missions.
Well, if you play on terrain bowling ball, yeah, sure, you can camp in your little shadow and snipe everyone in their bright light, but with terrain that often doesn't work. It's probably doable with a bunch of gals in flying armors, but I prefer other armors. Also, eventually you'll have to approach that UFO and playing "pickup the flare so I stay in the dark" is a very boring game, much like "playing fetch with flares while advancing in the shade".
Add the fact that sniping loadouts aren't particularly suited to breaching and that I prefer mid/close ranged combat, which, in the shade means stumbling on stumps or even trees and makes pathing and getting a LoF when you don't see the terrain. Having a "safe radius" of light around the gals to be able to play commando style
and seeing something, and having variations in light levels with different armors are an improvement over the previous situation for sure.