llms can handle greenfield stuff fine; it's just more important at that stage of development for the operator of the LLM to specify constraints where possible. If the operator is unaware of what constraints should be considered then they have an LLM right in front of them that is familiar with the idea premise that can help create constraints with the operator either via investigation, suggestion, or interrogation.

If the goal is "Claude plz make me a SOTA db system." , well -- 'garbage in, garbage out.'