I do find the sentence confusing, too.
How I normally would expect this construction to be used is like this:
Our hero couldn't have had a better start in life.
Which simply means that our hero had a better start in life than anyone else - or simpler: our hero had a great start in life.
In this case, the construction is comparing two characters in the narrative, though, where Subbu had a better start in films than our make-up boy.
I would have expected that to be something like
Our grown-up make-up boy's opening in films was nowhere as encouraging as Subbu's.
The construction as used in the text seems to want to convey the meaning that Subbu couldn't have had a more encouraging opening in films and that our make-up boy did not have such an encouraging opening.
I feel that by combining those two parts in one sentence as happened in the text drops some essential information.
I would have gone for the slightly longer:
Unlike our grown-up make-up boy, Subbu couldn't have had a more encouraging opening in films.
After re-reading the text, I think I am justified in finding the sentence confusing...
The next sentence (on the contrary...) forces me to re-interpret the original sentence in a different, more literal way:
It can not be true that Subbu had a better start than our grown-up make-up boy.
In other words, the author may want to tell us that is Subbu is doing well, it is not because he had a better start than the make-up boy.
It is a bit challenging to figure out from this excerpt what message the author wants to convey. At first I thought he wanted to sing the praise of the make-up boy by explaining how he worked his way up even though other, privileged, people had an easier start in their career.
On second reading, the author may actually be explaining that Subbu, although he was born privileged, actually didn't have a flying start in the movie industry, but worked his way up the hard way, just like the make-up boy.