Is it? If the security researchers don't find vulnerabilities, does that mean they don't exist? If the AI ethics researchers embarrass you, aren't they doing their jobs?
However they're empowered to fix them, essentially no questions asked. So you don't often get p0 posts about unfixed bugs in Google products.
I don't think OP is claiming that there ethicists have no skill, but rather that it's fundamentally a lot more difficult to evaluate.