This image claims that you can put decentralized apps (say, a messaging program) on the Ethereum network. It also claims that each computer on the network contributes a little bit to the processing of that app. That claim does not seem correct. Specifically,
I believed computation was expensive and anything but very lightweight logics (such as,
if condition is met, pay bob $10) could realistically be put on the blockchain. Not whole complex apps. Is that wrong?
I believed that every computer on the network performed all the historical computation of all apps, which opposes the view that each computer does a little bit of the work. If that didn't happen, what would stop a participant to lie about the result of a computation?