I feel this topic is complicated, because the way pokemon "evolve" should actually be considered "metamorphosis" because its is 1 species going through stages of forms that are specific to its species. The Different regional forms are represent true evolution, as the species have adapted to their environment and have changed in a significant way, and over a longer period of time, would become even more different. I say yes they are separate species from their ancestors, the Pokémon world has always had science wrong, like interactions between electricity and water. and electricity and ground. but that's a whole other topic to bring up. The real question is, why was there not a Dragon Gyarados in either game? But executor got to have a dragon type? makes no sense to me.
Volbeat and Illumise have sperate pokedex entries and names but are literally the same species, with different appearances based on gender
look at the nidoran family, they have seperate numbers for gender as well. Where do Nidoran come from? the female's cant breed! the males can breed, but their offspring is never a Nidoran?