Eh it really depends on the context. When I got my EE degree I was told getting your PE only really mattered if you worked on the power grid or similar. It wasn’t that you were less of an engineer or an expert without it but that 1) you didn’t need the legal ability to sign design documents most of the time 2) even if you took the exam to become an FE, the odds of you working under a licensed PE to get the requisite hours was so small it wasn’t worth the effort to take the FE exam.
If the case involved a field where a PE is standard, the expert witness should 100% have that license. However that’s a small number of sub-fields in practice and doesn’t necessarily correlate with practical experience.