If alien spaceships with tech more advanced than ours suddenly appeared in Earth orbit, you would conclude I'm sure that they're a potent threat to us even if you couldn't guess what weapons or what technologies they would use to destroy us. AI more capable than us is the same way: the threat is the capability to invent weapons and technologies (including weapons and tech none of us has ever imagined).
Inventing the concept of new weapons isn’t the same as building them at a scale capable of wiping us out. Cobbling together a human vaporizing ray out of toaster parts is pure fiction. You might as well worry about AI developing the ability to perform magic spells.
In reality any new weaponry takes time, space, and effort to build. The idea of an AI building secret factory in the jungle producing indestructible flying death cubes is the tech bro version of preppers who the woke up every morning worrying that Obama was going to take over and enact sharia law.
One argument (many years ago) was that no one would be stupid enough to give such an AI access to the internet or the ability to run code it has written. (In the HuggingFace incident, the AIs were given "read access" to the internet, or at least that was OpenAI's intent, but the AIs escalated that to write access.)
Worrying that an AI is going to figure out how to make a device that looks to everyone investigating it like a power generator, but once turned on kills all humans, is like worrying that an AI might discover magic. I can’t prove it’s not possible, but I’m not spending time worrying about it.
As weapons get more and more powerful they have always gotten more and more complex and required more and more time, space, money, and infrastructure to build and deploy. There’s no reason to think that this will change with AI.