No, the etymology isn't boring! (Or I'm boring for finding it fascintating, I suppose.)
The transition kicks in once the wealthy start having townhouses. They can no longer have their main meal (“dinner”) in the early afternoon when they'll be out and about, so the main meal often gets pushed back to later in the day. It's replaced by a smaller meal; a luncheon. “Dinner” therefore becomes something very often eaten in the evening, although “supper” remains if the evening meal is small (as its etymological link with “soup” would suggest).
The size of the meal traditionally determines whether it's a lunch / dinner / tea / supper. But plenty of people link the name with the time rather than the size, which is why we increasingly often hear of that monstrous meal which blocks up the toilets on Boxing Day being referred to as a “Christmas lunch”. Yuck. And even a carvery site will write this: