Simplest way to define a "destination wedding" is "some place I would NOT be going to at all if it weren't for the happy couple having decided to get married there".
Doesn't matter if it is Hawaii, Disney-XXXXX, a castle in Scotland, a historic church in (anyplace, really), or the side of a mountain - if it is NOT where I would pick to go at that time - then it is a "destination wedding".
I might decide to go to Hawaii, Disney-XXXXX, or the other places on a vacation - but I would be in charge of when I went, what I did, and what I might wear while doing it. It's doing it purely & simply as a wedding "guest/audience" that makes it a destination wedding.
Because while I'm at the wedding, reception, breakfast, shower, whatever else is going on - I am not "having my vacation", I am resting up for the next wedding event. Or after the last wedding event before going home...,
But if your niece who lived in NY married a guy from Kansas and decided to get married there , would that not fall under your criteria for a destination wedding? Even if every man in his family had gotten married In the same church?
I don't think I ever would have gone to Marysville, KS, if my husbands cousin hadn't married a guy from there. But that doesn't make it a destination wedding.
Nope - that's where one of the happy couple lives...
Maybe a slight adjustment to that "destination wedding" would be that NO ONE lives there, there is no history of the family living there in living memory (if you want to go back to "the auld country" from two generations back - that makes it a destination wedding - unless you have a surviving 118 year old great-grand-someone still living there who you want to have at the wedding, if at all possible - so they can see what their child's descendants are doing - taking a wedding to anyone over 90 or so is not quite a "destination" wedding, it is sharing the wedding with someone who would otherwise be unlikely to be able to attend - kind of a medical excuse, I suppose?).
So - no family living in the area, no close friends living in the area, no historical connection to the area (it's the auld country or the ancestral farm or something), and there is no pressure to do "wedding" the entire time you're there, so it can be a "vacation" except that there is a wedding to attend while you're there. Rather than being there JUST for the wedding...scenery, activities, relaxing, or whatever you'd do on vacation are not possible because there is no time or the visit is just too short to "have fun" AND attend the wedding.