Scorch is not that bad as of right now. If AA shield was improved to take slightly more damage that would be ok, but 50% damage reduction for 6 seconds? That would be awesome! Maybe too awesome, I'd use it all day. IMO the shield gives you an extra second of survival, a lot can happen in one second. Example: you can run and spam pots in PVE or in PVP chances of getting One-shouted by a rogue are lower.

Before the elite maps were reintroduced, I was a rogue without shadow piercer, and on the third map of tindirin, I had to use scorch's AA when i got pulled in. I didn't always get the shield up in time, but when i did it saved me from a death.