No that isn't correct. A hardware device can act as a black box however if the outputs are deterministic then the outputs can be validated. If a block box provides you a key how do you know it is random? The reality is you don't and thus you need to TRUST the results are truly random. However if you provide a black box which implements BIP32 (HD Wallets) a seed you can VERIFY the keys match the expected outputs. Single random seed -> a lifetime of verifiable results.
Of course! Verification of the results after applying a deterministic algorithm! You just recovered my interest in hardware wallets!
I remember a couple of projects in the Project Development subforum. One of then is/was Trezor. What is its current status? And, why is it so difficult (honest question)? I would naively think that with a Raspberry Pi, a LED screen and a cheap webcam (to send the transaction to sign) it could be done. What am I missing?