Blizzard
We've just applied a hotfix that reduces the damage dealt by creatures between level 1 and 100 by up to 16%, and their health by up to 24%. Until a subsequent fix (coming next week) to update clients with the new data, unit frames may not reflect the change in creature health, but combat should be faster and a bit less lethal across the board while leveling.
Thank you for your patience - we'll continue to monitor both logs and feedback closely, and will make further tweaks if needed.