Don't forget that most (all?) Dragons have a second type and there will (hopefully) be Fairies with some useful second types. Switch in with a Water/Fairy and use Ice Beam. I'm not saying this will be some fail-safe move to KO all Dragons but it's one example of Fairy type giving a distinct edge.
Just like how you can't randomly throw out a steel type against Salamence
That's because Salamence often packs Earthquake and/or Fire Blast. Dragon-types will find themselves soundly countered by a good Fairy-type if it exists with these type matchups. They'll have to start packing Steel-type moves like Iron Head to get a super effective hit in.
The introduction of a new type with an immunity to an older type is most definitely a nerf for the older type since it means that using moves of that type could give the opponent a completely free switch.