Of course it is. Just because Psychic has no effect on Dark types doesn't change that it works like:
Psychic > Fighting > Dark > Psychic
Defensive it's the same thing. All are not effective on the previous type.
About Fairy... let's see. Poison and Steel...
Poison > Fairy > Dragon/Fighting/Dark... nope, doesn't work. Steel > Fairy > Fighting... hmm.. well, since nothing is NVE on Fairy it's pretty much impossible actually. So the only thing we can work with is Dragon.
Fairy > Dragon > ... Dragon?
I guess it doesn't work.
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