Death Pact is a pain in the ass to manage because you have to go after creeps and then get back before it falls off. HotD ignores that because you can tell the creep to go wherever it'll be convenient for it to be. It essentially means HotD removes any downtime from DP while also significantly increasing the benefits you get from DP. It's not really unusual for Clinkz to get over 1000 HP from a big creep that's boosted by HotD and HotD's HP boost alone is worth +400 HP at lvl 16. It also turns into Satanic in the late game, which is going to leave Clinkz with a stupid amount of HP to work with, more than many STR heroes.
You could argue the lifesteal is weak in the early and mid game, but what else would you be building? 1800 gold for the amount of bonus stats it gives you is way too strong to pass up. You could get HotD later if you wanted, but why would you?