But what is The Witch of Mercury really about, other than some amazing mechas, which make for cheap, amazing looking merchandising? It's about a bunch of teenagers trying to live a good life in an apparently sensible high school/military academy, and having all kinds of positive dreams... while the reality is much different. Basically every parent is a manipulative monster. Everything that appears remotely positive gets crushed 2 episodes later. It's not a series about the wonders of the future. It's all about how the world is horrible, and no matter how much you want to pretend, the adult's horror has infected your world too. So even the the Gundam series you talked about is really about a dystopia where teenagers are turned into weapons by old people, and they will, predictably, have to overturn the old ruling class.
Not that Gundam was ever all that optimistic: Good old Amuro was the poster boy for the disasters of war back in the very first series. The fact that there's cool robots is just sweetener for stories that are mostly about dealing with betrayal and despair. It's not quite Grave of the Fireflies, but it's not any less grim than, say, Evangelion.