I think I've subconsciously made it one of my goals in life to disprove this, by finding someone on the other side of the world. I'm not getting my hopes up though.
First hand experience is that it can be very rewarding if the wave lengths match. It opens a whole new world of experiences and thinking patterns.
It takes a lot more commitment than, say, a relationship with someone from same college/town, so it takes more awareness about the fact.
Because when you spend enough time around anyone, you realize they suck (because everyone does). So some degree of grace is required as well to maintain love once the proximity factor has peaked.
I have two girlfriends who live two train hours away from me. As the two implies, I'm not living a regular relationship, so I'm inclined to go to greater lengths when finding someone that fits.
If you define proximity as spending time together IRL or virtually, then I agree.
[1] https://en.wikipedia.org/wiki/Mere-exposure_effect#:~:text=T....