Hate to break it to you but bearscream provides 3x damage, not 2x.
The rest of this i'll respond to later if i remember.
Oh. I thought they made it 2X a while back.
No it was originally 2X and changed to 3X.
Also i disagree with your ibg, i think it should not decrease unless it's above 1 IBG but if it's not it's fine.
As for shields i actually agree but it should be something more like 75% so it allows for pushes with 1 person tanking the hits but the other team can still counter by focusing them down. To give some numbers for this if you have 3 olivers going at another oliver with shields with spd sf hasr that's 174 DPS then turned into 40 DPS giving shielded oliver about 3s to live. So basically it means that someone can totally tank with shields but if they're on low health they'll waste the shields so you can no longer totally 180 by grabbing shields.