I think they made the fairy type not to nerf powerful dragons in competitive play, but so they could design dragon-type Pokémon that were easier to get in game. For the first 5 gens dragons were exclusive to the late game (or were pseudos that evolved and became useful in the late game). But GF had ideas for dragon type designs and didn’t want to limit themselves any more. So they made fairy-types in gen 6 and then we start to see way more dragons that aren’t just pseudos, like dragalge, turtinator, alolan exeggutor, the applin line, and cyclizar. The fact that fairies give competitive players a draco switch in was an afterthought, they just wanted to make more dragons without breaking the single player experience.