Who created which civilization, does not matter now.
Only thing matters which civilization you followed .
Some chose idol worshiping same as their ancestors(hindus ).
Some chose /got converted to a foreign culture (arab), some indigenous like late budhishm/Sikhism.
Hindus are called inheritor because the culture Hindus followed, is indigenous to land .
According to your indian logic,
if entire European continent converts to Hinduism, the Indus civilisation belongs to them?
Do you people even think before saying something?
You can change religion every hour of the day and claim the entire world. It's ridiculous logic.
It's time for you people to grow up.
Any claim falls into several categories,
Primary claim,
Secondary claim,
Tertiary claim.
Primary claim belongs to the land and it's people, nothing else matters, it does not change with religion, language or culture. Because these things are evolutionary in nature. The land remains constant and so does the continuous inhabitation by the people.
Secondary claim falls into various categories, for example, religion. History of early Islam happened on the Arabian peninsula, primarily claim to that history belongs to the people who have lived and still live on those lands.
Muslims from rest of the world can feel deeply rooted to that place in a religious sense but their claim at best is secondary, not primary.
Similarly, if today whole of India decided to become Jewish, it doesn't mean you lose claim to your own history. Religion is not the deciding matter, not even the main factor.
Tertiary claim can encompass distant links, such as the South Indians, In fact most of india can at best make a secondary claim or a tertiary to the Indus Valley civilisation.
The primary claim belongs to the entirety of Pakistan and merely the north westerns parts of india. That's it.
India has it's Gangetic civilisation, and the Dravidian civilisation, both of which have nothing to do with the Indus valley civilisation. Some influence is natural due to geography but that's nothing special.