The main problem I have with your argument, as much as it pains me to bring up hotrod memories, is that Kelly is the most marketable diva. She is over on both brands, fans support her and rally behind her, and she is much younger, prettier, and healthier than Beth.
No matter how good Natalya might be in the ring, which IMO is good while never showing the ability to be great, she has been there for years and can't work a reaction out of any non-Canadian crowd as a wrestler or manager.
Beth despite being kinda over really isn't where she should have been after they basically let her run through the roster when most girls like Maria, Candice, Mickie, etc were over. She is without a doubt the best regular worker in the division with McCool retired and Layla out, but that too isn't saying much since WWE clearly doesn't use her as their go to girl because she doesn't really have the looks to post on and sell magazines or cups, doesn't get the pops and astonishment like Chyna even when they put her in the ring with men to shock you, and she has been put on the shelf with the injury bug when they started to push her seriously on two different occasions. She even once stupidly fucked up the hottest diva the company had going in another big angle in Candice Michelle, and to be honest it was what happened after the injury that showed she really isn't a general who can think on her feet when she dragged her when she was clearly hurt and the ref had thrown up the x for what could have been a spine injury.
I agree they can squeeze more out of Beth, but her overall package really isnt one with a high ceiling that they can milk. She isn't overly pretty enough to pull off the spots Kelly gets outside the ring or LayCool and the Bellas for that matter. She really can't talk well enough nor is she comfortable enough in front of an audience to get the rise out of the crowd like Melina or Trish or Lita or Maria or Stacy or Torrie, and so on. Despite being muscular she isn't imposing as Chyna was to be taken seriously in the ring with men or strong enough to work with them regularly. She makes a great second heel diva to chase just like an angry Henry, Kane, Khali, or Big Show but her novelty wears off. She can even be the good heart warming story of the pretty girl without the looks who makes it to the too and gets a sympathy reign but the novelty wears off.
Natalya is everything i said about Beth, only worse in every area, making her a lite version
With Kelly you get the personification of diva, not woman's wreler.
If you want to see a woman wrestler look at shimmer, old ko matches, or even wrestlicious on mute. There are some great athletes and workers, but at the end of the day, most of them don't matter in the grand scheme of the history of the business more than being just another name working high school gyms, Internet ppvs, theme parks, and so on.
If you want to look back at who the mainstream fans be they faithful, casual, old, or new look at and remember when they think WWE females or female wrestling in general , they are Divas. There was Sunny and Sable who both couldn't work their way out of a shoe, but worked crowds into frenzies, got feuds over, and sold. There were women like Terri Runnels who got over the tag titles and vanilla/emo midget spot monkeys to steal from Nash, like Edge, Christian, Matt, and Jeff when they were young and floating much like teams like the Usos of today are. You can skip to Torrie and Stacy, both amazing lookers and talkers, who while just bra and pantie girls for a large portion of their career, could get anyone or any angle they were associated with over week in and week out (Maryse needs to take notes). Stephanie was very much a diva who could never really go, but her cat fights never lacked a reaction, neither did or does her mic work or appearances because she had an it factor to captivate the masses. LayCool were annoying silly, childish, petty, repetitive, and a cliche Mean Girls ripoff at times but they got a reaction on every show they were on, got spots in magazines, and pr events; same with the Bellas who were and are the wwes leading female ambassadors for make a wish and pr events. Lita was truly unique (like CM Punk) in her look, style of working, and the way she came across on tv before the Matt debacle. Lastly when you discuss divas, you have to look at the standard bearer which was Trish. Before her divas weren't expected to make big upper mid card money, go in the ring while looking good enough to take any photo and make it a mag cover, gain viewers every week over losing a portion of the audience, and be able to tug on the fans emotions; she truly changed the game much like Austin, Cena, Hogan, DX, and the nWo all did for their peers.
Kelly is prettier. Kelly is more over. Kelly is more marketable. Kelly is younger. Kelly has less injuries to her body. Kelly is just the better piece to build a division around than Beth who really offers you nothing over her but match quality, which last I checked while nice, never got the Bryans, Regals, Finlays, Pipers, Perfects, and DiBiases of the world the lead spot over the Hogans, Foleys, Nashs, and so on because at the end of the day the WWE is a business first and foremost with a bottom line they have to look out for.