This heavily depends on what project and stack you working on. LLMs are amazing for building MVPs or self-contained micro-services on modern, popular and well-defined stacks. Every single dependency, legacy or proprietary library and every extra MCP make it less usable. It get's much worse if codebase itself is legacy unless you can literally upload documentation for each used API into context.
A lot of programmers work on maintaining huge monolith codebases, built on top of 10-years old tech using obscure proprietary dependencies. Usually they dont have most of the code to begin with and APIs are often not well documented.