I think your confusng pessimism with scepticism.

Either his claim to take responsibility means something, in terms of it actually leading to consequnces and/or actions, or it doesn't. If it's the former, then what are they? If it's the latter, then why?

For example: do shareholders hold him to his responsibility? And if so, how? If they don't, who improves Meta's corporate governance to ensure that this self-admitted mistake doesnt reoccur and sexure their investment?

I've never worked at a BigCorp. How does this stuff work?