Personally it would make a bit more sense to make them not effective. I don't know much of the lore between dragons and fairies, but it's hard to imagine anything walking away from a dragon's fire breath totally unscathed. Is the immunity a deal-breaker for me? Absolutely not, and it shouldn't be for anyone else. It just means our Dragons need a diverse movepool, which is something I do with all my pokemon anyway.
Playing) Fire Emblem: Awakening, Guild Wars 2 Waiting) Pokemon XY
Assuming Fairy represents magic, it really depends on what fiction you're reading.
In some stories, magic is the only thing that can combat/withstand the might of a dragon In others, dragons are inherently magical creatures and are immune to others' magic.
But apparently Gamefreak is going with the idea that magic is the best counter to a dragon. So in that case, magic could very well be the only actual defense against them. A metal shield or armor could protect you from their claws or even their breath, but a ward or charm could prevent damage altogether.
Official Rinzler of the Kingdom Hearts III Board R - Hyuck hyuck hyuck!
Because Jigglypuff magically becoming immune to a Black Kyurems Outrage is all kinds of silly.
That's what makes it great
No it's silly. They go through great lengths to avoid doing something that "could" have been done in previous gen's. Like leafeon needing a mossy stone rather than just a leaf stone like the original eeveelutions etc. Or the Incense breeding stuff.
Now. Suddenly "poof" Jigglypuff tanks world shattering dragon attacks for no reason.
I'd be totally fine with it resisting dragon. But Immune? No.