I know three chinese are the HOD in Petronas, and one of them have been working in Petrons for 20 years, I don't think if the environment is that awful you could stay there for 20 years.

You may not see many Chinese in twin towers, because majority of them are Bumi (quota maybe), I met some of them are actually very well-verse and capabale (As you would understand not all Chinese are hardworking either)

I do not know what's their salary range but I heard the bonus and medical coverage is good , except some of the Petronas staff complaint to me about the annual leave (about 14 - 16 days if I am not mistaken, for me is decent anyway)

Imagine Petronas could be in profit for quite some years consecutively, even when majority of them are Bumi, I am sure they only pick the good from the pool (Think about MAS who always loss in contrast).