That you have no idea how much revenue is attributable to you as an individual doesn't mean revenue in general can't be measured and attributed.
Hypothetical example. Your employer has 1 billion users. You create compression that cuts down storage costs by 4%. Run the math and you see how much you saved.
If you saved $0.01 per user, you saved $10m. If the average salary is 100K and you saved $10m, you performed at 100x.
I agree the potential for "X" performance is hard to spot or measure when one isn't in proximity to big problems.
The key claim is: there’s no way with any reasonable amount of resources that you can guarantee that the software and hardware are bug-free and that they haven’t been maliciously attacked
The same could be said about other electronic systems that already govern lives, like planes, cars, phones and medical equipment.
https://en.wikipedia.org/wiki/Apple_I