>>32726312With its overly feminine design and dex entries revolving arond reverse harems and pheromone control, you might argue gamefreak really just wanted a lizardbait pokemon and there's nothing deeper about it, and you wouldn't necessarily be wrong; they might just be trying to appeal to furries and scallies for all I know.
However, I think salazzle's true reason to exist is that they wanted for Plumeria's ace to be analogous to her role and thus they came up with a lizard big sis (plumeria) that controls tiny little thug lizards (skull grunts). Salazzle even has similar pink marks reminescent of some of Plumeria's clothes. Also, do note that literally no grunts during story mode use salazzle at all, this is a mon only Plumeria uses within team skull.
The same way, I think Gardevoir, which for most is the "original waifubait", was just made inspired by a guardian angel, as it was to become Wally's ace in RSE, and he being a sickly child, gamefreak might have felt a guardian mon would be appropiated.
I honestly think most of the time gamefreak designers are just incredibly, extremely innocent and oblivious to what weird things the fans will feel about these mons. On the other hand, there are times where it is incredibly difficult for me to believe that they don't know what they're doing, like when they make mons like Lopunny or Tsareena, for example. Each designer might have different goals or demographics, who knows.