Yes and no. Yes, you actually have to kill to get a shield with potentially the same base protection as the warlock's. However, the shield the warlock gets is not purely the skill itself, only a perk of the overall burn melee. They could also choose to push enemies with it, potentially off the map, and something else I forget off the top of my head. The scorch shield simply offers better survivability. The titan gets the shield on a kill no matter what they have as the chosen perk, meaning it balances out quite well. The last one gives you a constantly regenerating over shield. Combine with No Backup Plans and you're a pretty tanky fellow until it goes away in about fifteen seconds. Overall the only thing is that the warlock provides instant gratification whereas the titan requires a bit more patience and concentration to pull off.