Concise, jargon free or limited explanation is the opposite of dumbed down. It requires to most skill and understanding to do well. Opus 4.8/5, for whatever reason, are getting worse at this crucial skill.
Effective jargon usage is understood by the target audience.
If the AI is communicating to me and can't select the appropriate jargon level, it's failing at communicating effectively.
Or you're below its level.
As long as the linguistics are the issue rather than raw inability to understand the concepts being communicated, then the model is just being a bad communicator.
That's a loadbearing, heavy shaped, second take worthy statement