The one you're describing is the pull down. The AI doesn't need the library as a comprehension aid, so it drops a layer and writes the ten lines it actually needs. There's a second reason it might do this: it doesn't trust code written by other AIs, and pulling the functionality in-house shrinks the surface area it has to reason about.
But there's also a pull up. Writing code is getting cheap; making it hardened may not, and that gap doesn't close just because token prices do. If that holds, the economical arrangement is that someone (OSS or SaaS) ships vetted blocks and each user grows their own feature layer on top with their own agent.
Which means the stack gets taller rather than flatter. The top layer is bespoke per user instead of shared, and the bottom layer matters more, not less, because everyone is depending on the same small set of audited pieces.