The other thing about the weight designation in the US was that eventually, most outfits stopped trying to do multiple non-heavyweight weight divisions. Some territories may have had two non-heavies (I believe it was rare), but most decided to name their juniors welter/cruiser/light heavy as the non-heavyweight wrestlers for the most part.
The biggest thing that is probably missing here from a cultural standpoint that might help David (or at least I didn’t see when I skimmed this thread) was that in America in the early part of the century, boxing was king, and being the heavyweight champion of the world meant you were the most popular athlete in the country. As big as Babe Ruth was, there was a level of fame being the heavyweight champion that was unmatched.
With pro wrestling being presented as trying to be somewhat legit relative to boxing around that time, and those earlier matches were seen as competing against the big boxing fare, wrestling tried to mirror that to bring in a lot of the same crowds when they could, and that meant they needed heavyweights to draw against.
Thats not to say the lighter wrestlers weren’t featured, but as heavyweight boxing took off and became the defining sport of the first part of the 20th century (while baseball was popular, the biggest boxing matches were normally more popular), I feel there was a template in place once the NWA took hold and tried to match up similar to the boxing federations.