It's even harder to imagine India without chillies.

India used black pepper before chillies so things were just as hot. Just a different kind of hot.

putting an extreme amount of black pepper in a dish does not make it unbearably spicy, it just makes it taste way too much like pepper.

theres definitely no way black pepper can be "just as hot" as chillies

You haven't used really hot black peppers then. Also I say black peppers but also people used cloves and bay leaves.

It is a different spice so yeah, it doesn't burn the tongue but just heats up your body.