>>40783510No, Gardevoir has curves, but they are not as obvious as they are made out to be in most of the arts.
That being said, my headcanon is that after mating with a human, the resulting Ralts will still be a Pokémon and evolve as such, but it will have more human qualities and being able of human speech alongside psychic.
When the Ralts evolves into a Gardevoir and mates with another human, the result will still be a Ralts, but with even more clear human qualities.
However, no matter how many new Ralts are born this way, they don't become half-breeds. They remain pure Pokémon, albeit with slight differences in appearance.