First off, if you're playing someone way above you in LP and you lose, you lose like 5-25 points. It's not worth rage quitting over. Secondly, while I've never quit a match for any reason whatsoever on purpose, that level of lag is a bitch and makes the match useless.
I've lost probably 1500-2000 points based on rage quitting, but none of those guys, absolutely none, quit before I beat them. I wouldn't blame a guy for quitting who had 2000 LP less then me and lag started. It's actually better for me tbh. I stand to get like 25 points but stand to lose like a 100