Can you host files cheaper than Dropbox? Of course you can. :)
Once you discover what the useful problem to solve is and how to utilize it in production, you can of course replicate it.
This is not alchemy taught by some wizard in secret.
Very often, the innovation is in identifying what to build, what has interesting use cases, what people will pay for.
Once this is established, there is further research optimizing it further, replicating it locally, etc.
The fact that anyone could have come up with it is irrelevant.