That would be neat, but given they were clearly trying to subvert expectations of common conceptions of the Norse, and instead have them be the bad guys, and the giants be the good guys (or at least not the raging assholes that the Norse are), it makes sense to have him be a half giant, and that makes him being Loki work really well narratively. Especially if you already know you are building towards Ragnarok, which they clearly were, given it's the central, driving force for the entire conflict with Freya and Baldur and Kratos. That way, you can set it up to have things go to shit at the end as sequel bait, and still keep to the prophecies. If Atreus was Arrow Odd, while that would match his MECHANICAL place in the game, it wouldn't really mean anything in the narrative sense. Because as you put it, nobody really knows about him, outside of mythology enthusiasts. Which, most people aren't. I would say that I've got slightly above average familiarity with norse mythology, compared to your average Joe American, due to my history as a roleplayer of games that focused on that setting (Scion from White Wolf in particular), and some fantasy novels that dive a bit more obscurely into the lore, so I can recognize a few odd ball myths here and there. But I'd never heard of Arrow Odd. So it wouldn't really do anything for the audience. It wouldn't give millions of players that "Oh shit!" reaction when they learn the truth at the end, they would universally say "....who? Arrow Todd? Who the fuck is that?" And all emotional investment of that touching moment, leading up to the reveal, would be dashed on the shores of audience confusion. And lose all the lightbulbs popping off in people's heads, as they connect the dots, and have that nice endorphin rush of seeing The Twist, laid bare in front of them and what it means going forward. That's just bad writing....so don't do that.