I don't want to be rude, but you're not the only smart person who's thought of counterparty risks. There's tremendous incentive to all sorts of people to break the cryptographic security that secures these networks. And, thus, also incentive to stay ahead of those people.
I'm not very worried about the cryptographic security of the Bitcoin blockchain.
I am worried that in 5 years we will learn that some hardware wallets used side channels to transfer bits of your private key out to make it easier to guess for someone who worked at the manufacturer.
But you can check this. You can monitor whether info is leaving on other channels. And you can sign on an air-gapped computer and transfer only the signed transaction hash (never the privkey) to a connected one to broadcast. You can do all but the actual signature with open source tools.
Just because you haven't taken the time to learn how this stuff works doesn't mean there aren't thousands of incredibly intelligent people who have been working on it for a decade and have actually solved the low-level concerns you have.