[rcacho]

It seems like you are imagining that highly prized engineers are valued for their ability to write bug free code or have their code correctly meet expected requirements.

This individual is likely being paid this amount because of their ability to identify and solve difficult problems. There aren't guardrails for that sort of thing.

As to their replaceability, I think it's a case of it being a safe option. This person has proven themselves, through their experience, that they are worth this amount. There may be others out there who can do the same work but they haven't "proven" themselves.

Whether the value obtained from an engineer paid this amount is worth it is another question. Are they providing twice the value of an engineer paid $445k? Maybe not, but this person is in a better place to negotiate.