I disagree about the crit changes, I'm really excited about them. Being able to get a defensive item that protects you against burst specifically as your FIRST item without screwing up your build or scaling at all is spicy.
I do agree that damage needs to come down across the board, but assassins will need to be compensated. They walk a razor's edge of damage thresholds. If they don't engage and get a kill, they die. It wouldn't matter that damage got reduced, because 3-5 people shooting at you still kills you, so if you go in, dump all your cooldowns, and don't get a kill as an assassin, you are worthless to your team. Assassins would need to be retooled around either chunking somebody and retreating, or finishing off enemies who are brought low and try to escape. This means a buff to their mobility, either in the form of target access or their escape. Their job wouldn't be to 100-0 people, it would be to 50-0 people and make it out alive.