Blacksmith specialty is boss killing due to his HP% shred on his 3rd ability. Due to this max his third skill before anything else. I recommend stacking attack and crit to maximize the damage on his 3rd skill. His passive has great synergy with his shred making him quite tanky as well. However he lacks utility and doesn't offer much in the way of range or AoE. That what keeps him from being 10/10.
Verdict: Blacksmith is a total BA and should be a permanent fixture in your team at least until he is 5 starred. After that you can swap him in as needed for boss fights.
