That just means that the edge you’re able to retain if you invest $1B is nonexistent. It also means there’s a huge disincentive to invest $1B if your reward instantly evaporates. That would normally be fine if the competitor is otherwise able to get to that new level without the $1B. But if it relies on your $1B to then be able to put in $100M in the first place to replicate your investment, it essentially means the market for improvements disappears OR there’s legislation written to ensure competitors aren’t allowed to do that.
This is a tragedy of the commons and we already have historical example for how humans tried to deal with it and all the problems that come with it. The cost of producing a book requires substantial capital but the cost of copying it requires a lot less. Copyright law, however flawed and imperfect, tries to protect the incentive to create in the face of that.