I'll give my view as a half Kashmiri half Punjabi Muslim. I do consider myself Muslim first and that's because it shapes my day-to-day life vastly more than my ethnicity does.
I agree with you that a Punjabi Muslim has far more in common with a Punjabi Sikh/Hindu than a South Indian Muslim. However I have far more in common with a Punjabi Muslim than a Sikh. Religion isn't a small thing as your comments (perhaps unintentionally) makes it sound, it shapes culture and worldview.
One of my oldest friends in actually an Indian Punjabi Sikh, I've known him the longer than any of my other friends that I'm in contact with, but there are still massive glaring differences. He drinks a lot, I don't drink at all; he can eat any meat, I can only eat halal. Then there's religious holidays, we only celebrate our respective religions festivals. Really, there's not all that much in common. I speak Urdu instead of Punjabi which also contributes to that. I'm actually not sure myself how we've been friends so long tbh lol. I've even lost contact with some Muslims because I had nothing in common with them personality-wise, religion isn't enough for friendship but it's a good starting point.
I'd be happy if there was more tourism between the two Punjabs, but I wouldn't suuport a reunification. I personally have no interest in visiting the Indian side.
I think the similarities get over-exaggerated, but much like it was to Navjot Sidhu, south India would be like an alien world to me.