What would happen in aot humans found energon and reverse engineering then advanced their technology to combat titan before Optimus came to aot world?
Hm. It's an interesting thought. (And sorry it took so long to answer. I've been busy.)
The thing with energon is that the Survey Corps are not actively looking for it. They don't even know what it is. So how do they even come across it.
Enter Ilse Langnar
See when Ilse's squad gets attacked, leaving her the only survivor. She runs away and stumbles across a small pocket of energon. She notices the way that the titans avoid the energon. She tries to take it with her bare hand, but it burns her. But she knows that if she doesn't take it, she will die. So she tears off her cloak, picks up a small piece and wraps it in the cloth before tying it to her person. She continues running to the wall, noting the way that the titans continuously avoided her. And instead of dying by the talking titan in the OVA, she makes it to the Wall alive.
The Survey Corps are stunned to see her alive. How did she manage to survive in titan territory for weeks?! Ilse gives her notebook and even shows the energon that she found, explaining that this rock saved her life. Erwin immediately allows for another excursion to a) try and find this rock, and b) to capture more titans per Hanji's request. If energon is posing as a deterrent or even a weakness to titans, this is a major game change.
Erwin still suspect fowl play from the government, so he keeps this resource among the Survey Corps only. But through the sample that Ilse had taken, Hanji finds out that the energon is highly flammable and explosive. Meaning that it could be used as a weapon. Once Ilse guides them to where she found the first batch, Hanji immediately tries to create new weapons. During a titan experiment, Hanji uses a flare gun that has energon embedded in it and shoots it at the titan's face. They think the titan will be fine, but the titan ends up dying on the spot. And while Hanji is devastated at the fact they killed on of the titans they were bonding with, they just killed a titan. Without hitting the nape. Once Hanji gets over it, they tell Mobilit to:
The energon is a literal game changer! And now they cannot keep it underwraps from the government because there were some MPs who saw the commotion! The crown of course wants to get rid of it to keep control of the people, but Pixis and Zackley make a joint decision to leak it to the public, immediately gaining their support. The government has to work behind the shadows to smear the Survey Corps name. They even send spies to figure out what the Survey Corps is making.
But with this resource, mortality rates in the Survey Corps have decreased substantially. They’ve managed to secure a path to Shinganshina and make plans to seal the hole in the gate. They’ve even managed to kill titans from long distance with flare guns.
Of course there’s still the matter of where this substance even came from. Because it’s not a common resource or element for humans. It’s clearly not organic. So what the hell is it?
They get their answer when Optimus arrives in Trost a few years later. He kills the titans with weapons that mirror the energon flare guns. His eyes glow the same hue as those rocks. And Optimus says that he’s from another world. He has the answers to the humans’ burning questions and the hope to permanently bring an end to this conflict.
Although Optimus is going to have an internal panic attack when he realizes the humans have been tampering with energon.
Hanji: Oh yes! The blue fire crystal has blown up in my face multiple times!
Optimus: *external panic*
Meanwhile Ilse actually thanks Optimus because his resource saved her life.
