We all can agree that Nuclear option is a sort of a great equalizer. It is kind of a bullet or poison dart. With that even a weak old cripple can kill a macho WWE winner.That is the point. If India is under the perennial insecurity of losing Mumbai or Delhi then your phrase "Complete Domination" in conventional forces means nada. Insecured people with fancy toys do not win the wars. Look no further than GCC.
Actually 'Complete Domination' still means a lot. If your opponent has to use nuclear threat on every single agenda then it becomes a global boogeyman. So, even in peacetime people have hard time investing and associating with such country. The country goes crazy and it can blow up itself with your investment. Ever wondered why China keeps such a tight leash on Pakistan and punctuates her nuclear cries everytime? Pakistan is a monkey not only on our backs -- because of her Nuclear war-cries -- it is a monkey for Chinese banks too. A rabid monkey which is needed to be kept on tight leash.
In the common analogy, it is same as a person who brandishes a gun at every party they visit. No one invites them to their party and those who have to, need to make them suite up in a straightjacket.