That's of course rather nonsensical.

In a "one LLM only" environment, your instructions are by default tuned for said LLM.

In a multi-LLM environment, roughly nobody will keep separate sets of instructions for each. It's not a realistic take.

On top of that: If your LLM is so bad at reading that it can't follow a set of instructions that wasn't specifically written just for that one single precious LLM, I sure wonder what that says about your employers repeated statements that ASI is definitely right around the corner.