You're right; it is important to note that the Pixel is not entirely vulnerable to water. I think most people worry about the dreaded phone in the toilet (my wife did that a few years back). Submersion means death without an IP66 or better (on paper, anyway). As for a dust rating of 5, that's kind of ludicrous at this point in the smartphone game. Fair enough, it really doesn't make THAT much of a difference, but when we've seen phones come out this year, all with IP67 ratings, 53 seems like a distinct decline.
Again, though, I totally hear you. I'm of the paradoxical mind that I want the better dust- and waterproofing because I'm paying such a high price, but really at the end of the day what does it matter? Well it matters because these things cost as much as iPhones. Fine, but have you ever gotten a phone wet? Well no, but... And on, and on, and on