Had time to play most of the game modes now and assess the changes and looking from the point of view of the OP i can understand why the changes were made however the consequences these have had on some game modes is crazy.
Arena seems like the mode that has come off best from these changes, i can see where these changes are heading and it's the right direction in my opinion, however your character balancing needs to be quicker as people like fives can't go on like this for long.
Galactic war is a simple fix in my honest opinion just reset the teams overshield and not health at the start of each node, this was already pretty fair after the matchmaking changes and this would revert it back to that with the slower fights that you wanted. Making a team chew through a shield every round that they don't have just seems to make it pointlessly harder.
Story battles need tuning and quickly, some nodes are nigh impossible at the levels intended to do them and banging your head up a brick wall in such a simple part of the game is a big turn off.
Last but not least the challenges.....my god how these got past testing is beyond me, they are brutal and re-doing the same thing over and over again until the RNG gods shine on you is not fun. The tank only challenge was already horrendous before this update i can only imagine what it's like now after seeing the healing/support one today. Nerf them and fast.