Guardrails are a rough analogue to binding parameters in SQL perhaps.
These methods do work better than prompting. For example Prompting alone for example has much poor reliability in spitting out JSON output adhering to a schema consistently. OpenAI cited 40% for prompts versus 100% reliablity with their fine-tuning for structured outputs [1].
Content moderation is more of course challenging and more nebulous. Justice Porter famously defined the legal test for hard core pornographic content as "I will know it when I see it" [Jacobellis v. Ohio | 378 U.S. 184 (1964)].
It is more difficult for a model marketed as lightly moderated like Grok.
However that doesn't mean the other methods don't work or are not being used at all.
[1] https://openai.com/index/introducing-structured-outputs-in-t...