[DuncanWaring]

At 6,000-tons, this sub will be pretty small when compared to US Ohio-class boomers, ...

True, but recall that the USS Nautilus (SSN-571) had a displacement around 3500 tons.

[sukhoi-30mki]

The French navy’s Rubis class SSNs are even smaller at around 2,500 tonnes submerged displacement.

But then these were not SSBNs(if this Indian sub actually turns out to be one).