Except for the part where Marley is the one MAKING the Titans. Like, the Eldians don't just become titans on their own. They become Titans because the Marleyans inject them with Titan juice to turn them into weapons.
It's like if the world feared Jews because they were also nukes, but the Nazis were the ones turning them into nukes and launching them at people.
Falcon's heel turn is dependent on what happens to Gabbi. It's obvious she's the one he cares about, and if something happens to her, that's the thing that will send him into a hate spiral.
I mean, you're metagaming there. Atomic bombs might never be invented, and they certainly wouldn't KNOW that a thing they can't even conceive of is going to be invented.
But you are right that technology WILL surpass the Titans eventually, and they probably WILL come for them.
Of course...the solution there is to...also progress your technology, and not rely on the Titans for your defense.
Aren't the walls made up of, like, a million near-colossal Titans that the entire reason Paradis was left alone was because the Founder could wake them up and wipe out the world at any time?
Again, though, that...doesn't happen. Like, nobody inside the walls ever just spontaneously transformed into a Titan.
The Titans were all outside the walls, and they were there because the Marleyans kept making them and SENDING them there. If you don't have people running around injecting Eldians with needles full of Titan fluid, you don't have people turning into Titans.
Well, Armin and Erin DO know that. They're Titan shifters. Which means they're dead in a couple years regardless. And then Mikasa is all depressed because, well, the only two people in the world she cares about are dead in a couple years regardless.