Hmm... let's see. The half-bloods are a strange lot, powerful enough to have a triple mark and 200 HP, but weak in that they have no united strategy and don't have all their cards upgraded.
I think the sole reason Zanz added Half-Bloods into this game was as an encouraging element in the game. Now that it is considerably harder to win against False Gods thanks to the Dial nerf, new players need something to aim for, a goal that they can reach to bridge the considerable gap from Level 3 to False God. That bridge is the Half-Blood - considerably easier to beat than False Gods but also considerably harder than Level 3s.
And the rewards aren't that much greater than Level 3s, either. You get more Electrum and a small chance to win upgraded cards, but that's about it. Let's put it this way: if you find yourself consistently winning against Half-Bloods, fight False Gods instead. The rewards are greater and if you have enough power to farm Half Bloods, False Gods will give you a greater overall profit.