You are right when you say the nikah is NOT valid and this kind of marriage is not recognized in Islam and both are guilty of Zinna. But most muslims who marry Hindu or any non-muslim for that matter isn’t really practicing Muslim anyway. Would it make any difference if SRK married a so-called muslim woman? He is still doing all those sinful things like touching half naked women and dancing with them, drinking, so what differnce does it make if he’s marrying a hindu? I have never seen a hijabi woman marrying a hindu man or a guy with a beard who prays 5 times a day marrying a non-muslim woman. The only people who are in these marriages are totally nonreligous people who just have a Muslim name, thats it.
I see it as a positive thing since inter religous marriages brings more tolerance in my opinion but I can see why people are outraged since it’s unislamic. However I don’t see so much outrage against muslim women dancing with na mehrams at their cousins weddings on inappropriate indian song lyrics wearing capris and no dupatta and free mingling between na mehrams everywhere. So in the end everyone just draws the line somewhere..