Of course my computer is not immune. The difference is two fold. One, I am in complete control of my data. If I want to be super paranoid and have my 1P vault stored on a computer that is always disconnected from the internet I can. Or I could run it in a fully isolated VM. Two, and this cannot be overstated, my computer has an infinitesimally smaller attack surface than 1Password's servers have.
The bottom line is this - by forcing its user to store their password vault on a cloud server, AgileBits is decreasing the security for its users. Full stop, end of story.
Whilst you may perceive your last sentence as true, I’d love to explain something a security expert explained to me:
Time and resources taken to try and access your files and passwords stored on your device would equate to roughly £90,000.
Time and resources taken to try and access your files and passwords on a 3rd party 3-key encryption would equate to £3,000,000.
I would have to be certain, in both regards, that your passwords are worth at least £90,000 for it to be worth it.
Her point to me was that whilst having it stored locally is still a large undertaking for criminals, having it stored otherwise is a bigger deterrent.
It was interesting to chat to her. So yes while you perceive your choice to be MORE secure, it is no MORE secure than the other option and in some regards, has less deterrents in front of it than storing otherwise.
I once knew someone who used a password manager, stored locally and had a YubiKey. He was robbed at knife point in a cafe! These thugs are starting to get wise, sadly!
edit: they even took his cap and watch. Ridiculous!