Lol you think private sector doesn't have nepotism? This is India, if you are willing to get taken advantage of you will always be taken advantage of. In gobarmint you have a choice, like you said you can just fuck off after office closes and they can't touch you, if you do this from the very start they won't get pissed either.
My dad was a workaholic and he got a top tier position that wasn't even technically for his service because of it that let him eventually take VRS in his early 40s and open up his own firm. My mother was in the same service and same batch, she would do her work but not go above and beyond, so she just kept getting promotions normally. Now that she's nearing the top she often needs to stay after hours but before this, other than on March 31st, I can't ever remember her being late.
Which Indian office even pays overtime? I talk with people at our networking parties and literally the biggest, most prestigious firms still expect you to work 80+ hours every week for your first five years at least.