If there was no nepotism or favouritism...

...Who would emerge as numero uno in Bollywood? Based on sheer merit alone?

You have to pick an actor and actress both.

What about box office and acclaim ?

Alot of "acclaimed" actors have shit box office records and blame nepotism and audience.

It’s not possible. Nepotism and favoritism exists because it’s human nature.

Hypothetically if it happened then not sure about Numero Uno but Kangana would definitely not be famous and same goes for Alia.

Kangana is famous because of Nepotism and so is Alia. Kangana speaking against it is hypocritical to say the least.

This is impossible to judge because natural human behavior is to always gravitate towards people that you like. It's why networking in any profession can often take you even farther than just pure merit. We tend to think of actors based on the pure acting talent but networking, building relationships, backing good scripts, marketing, etc. are all equally important skills required for success.

That's why I believe that most stars would more or less reach where they are today. Their journeys would be longer without nepotism at play but if such a large section of the audience and/or industry is appreciating you, then they would have seen those same skills eventually.