As we've seen with our space probes, its difficult enough to land something on another planet and have it survive, nevermind equipping it with any offensive or defensive capabilities. Maybe these aliens are in the same place. They can get the balloon here, but just barely, and they're watching in dismay as their work get dismantled.
Utter nonsense. This would be a FTL alien civ. A civilization with many orders of magnitude more energy available. And manufacturing capabilities. And AI. And many other things. They’re not gonna send a stupid balloon. They’re not going to care about a balloon. It’s inconceivable that a civ could get here and not also have the ability to manufacture such basic technology on an enormous scale very easily.
Breakthrough Starshot is about sending a couple grams of tech on a multi decade journey. We are very far from having the tech to do this. You’re right. They don’t technically need to be FTL capable. But the rest of it remains. You’ll need an immense amount of energy move this far.
If you can get balloons into earth safely, you can also just pelt the planet with big chunks of metal at speeds more deadly than nuclear explosions.
