I've been searching the workshop waiting for someone to do something to improve flashbangs. While my complaint isn't towards crits alone, I am left wanting more out of flashbangs. It angers me to no end when I FB (flashbang) the enemy and they continuously get hit after hit on me. I swear its 8 out of 10 times and its infuriating.
What I propose is, not only do they have a reduced, to thier already, reduced chance to hit/crit/movement but also a reduced sight radius. So my soldiers who are fruther than 5 tiles away would be virtualy invisible. Come on modders, this has to be possible.

I have been having a good amount of success using : "Enemy Unkown Aim Rolls"

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=624799134

From the description:

"Separates the rolls for hit, crits and dodge.

Gone are the days of troopers having 100% crit against people in heavy cover + aid protocol, since in XCOM 2, hits, crits and dodges shares a single roll, so if the crit chance is higher than hit chance, it always crits as long as the target can't dodge, dodge is less affected because the dodge roll is calculated based on dodge stat * hit chance. "

This workshop mod fixed this particular annoyance for me. Give it a try. I no longer fear throwing flashbangs and seeing CRIT CRIT CRIT in return.

They can still crit, but their chance to crit is their normal chance, not 100% on a hit. It becomes a separate roll entirely like it was in Xcom:EU. For example, a flashbang reduces their hitchance but not their critchance so like OP said, every hit becomes a crit. With this mod the flashbang lowers their tohit chance, but the chance to crit is untouched and rolled separately.

I think this makes the game play as it was meant to be played. No idea why they tried to double up hit/crit chances into one roll.