It's a very valid point and I appreciate your knowledge. Back then, following things were different.
1) Russia was backing India.
2) Russia was Second super power
3) Russia had nukes, though India didn't have that.
4) China wasn't super power and a technological power.
Now, do the analysis again. It's the other way round.
1) Russia won't back India if China were to fight India.
2) Russia is no longer an economic or tech super power. Its still struggling.
3) Russia still has nukes but for what? They won't use on China for attacking India.
4) China is a world super power, be it economy or technology.
Same odds which were against Pakistan in 1971 are against you. If there is a conflict, you can kiss good-bye to many of your provinces/states. I'm not trying to mock you, be realistic. India can't fight China.