Well, like you said, he's correct. It's not about racism or anything, but the statistics and anecdotal evidence speaks for itself. Western culture in general has normalized divorce and advocates an individualistic perspective that de-emphasizes married life compared to most traditional cultures, including Desi ones. I'd bet that most American-born Desis have higher divorce rates than their folks from India, but still not as much as white people because their extended family (aunts, uncles, grandparents) still holds divorce as a stigma.
Of course, statistics are generic and don't account for outliers and other factors. I'd also warrant that your parents had an arranged marriage, not necessarily a coercive one, but one in which the cultural expectation is that marriage is sort of a duty in one's life that you just sort of adapt to. If there were huge objections, they wouldn't get married, but there wasn't a dating culture back then where you got to gauge someone for years for compatibility before tying the knot. To that extent, marriages were also a sociocultural affair, and not informed by individualistic feelings of love the way they are now.
Considering you don't have a specific example and are just talking in the generic sense, this all makes it harder to generate specific arguments. The line of defense I would use is:
-You grew up in the West, and so have any Punjabi girls you would potentially date. Even if you hold some cultural baggage, that culture of individuality > family ties is prevalent in the West, both among you and among any Punjabi girls you see. I.e., you and your GF need to be actually "compatible" and get to know each other and can't just adapt the way your parents may have been able to.
-The dating pool of Punjabi girls is extremely small in America, so the probability I find someone who is "compatible" with you is significantly smaller in America, and there's a good chance it'll be someone from a different culture.
-Maybe you could emphasize how not all white people or whatever are the same and have the same values (because they're definitely not, again stats show overall trends not specific individuals) and that if you're dating someone and are compatible enough to marry them, they're probably going to end up sharing your values as well and aren't just going to be completely out of left field
In reality, knowing most Punjabi parents, they'll probably be fine, especially with goris (some of the more anparh folks would have an aversion to blacks, good ol' racism at work, but your dad seems to be reasonable). My own father is extremely liberal and had a love marriage, so he knows what's up. His only real condition is that I marry someone that's educated and not a complete village idiot.
We have discussed dating "out" before, and he's absolutely fine with it in principle. However, he told me to note that while there are lucky cases where things work out perfectly, there will often be tradeoffs and you should be prepared for that. For example, I feel pretty strongly about my faith (Sikhi), so I don't think I'll be marrying into a Muslim family, if I can help it.