Man, I honestly don't think Attack on Titan is really one of those 'deeper meaning' animes. I haven't read the manga or watched the anime myself, but from what glimpses I've seen I simply can't interpret it any other way aside of "these guys are being hounded by giants. shit happens. more, crazier  shit happens".

I'm probably biased though. I can't form deeper meanings myself I think, so I'm obviously not very good at detecting existing ones either I suppose. So take this with a grain of salt.