If LLMs can't deal with those legacy file formats, I don't trust them to be able to deal with anything. The idea that LLMs are so sophisticated that we have a need to dumb down inputs in order to interact with them is self-contradictory.

While I agree, the parent also talks about efficiency. If a different format increases efficiency, that could be reason enough to switch to it, even if understanding doesn’t improve and already was good before.