For the most part I completely agree with you, and I have absolutely no problem with the cooldown on Grit, because in all honesty I rarely Leave Grit + Darkside.

The Problem here resides with how you changed DP and TBN.

For DP: A 15s blind is far more useful than a 5s stun with how the game is right now. If they just make it so that blind is included into the base effect, I would actually use it. Blind is fantastic damage mitigation with how accuracy is right now.

For TBN: In all honesty, all I would do to change is increase the duration to 6s ~ 8s and increase the cool down to 20s ~ 30s which would balance it out more by making it unavailable for every tank buster. Have it spread to nearby allies would just out right brake what little balance the skill has.