If someone says they are an expert at nuclear engineering, I expect they can build a working reactor in their basement, not that they have read a pamphlet and might know the difference between fission and fusion.
Let's be honest here: both sides of the case want "their" expert to testify. I.e., someone who has enough knowledge on the topic to push the given narrative convincingly. There is a massive difference between a court case and actual science.
The court does not need to build a nuclear reactor. They need someone who can help the court understand nuclear.
Your theoretical person may be a bad choice if they have no communication skills.