Some of them are, some not. But if you look at them and other types from purely an stereotypical point of view, they are well above average of all types, because of this mysterious aura that they have and im not sure if its just a coincidence that i got this view of them, but they seem to be submissive kinks really often. I think its about the nature willing to please that makes the submissiveness and inferior Se easily leads to kinkiness.. Not that a submissive kink is some ultimate turn on for me, but..
"Where wisdom reigns, there is no conflict between thinking and feeling."
— C.G. Jung
I am not sure if "sexy" is the correct word - we are talking about personality here while the term sexy carries a lot of associations with visual appeal - so I would rather use sexual (Although it's possible that an advantage in self discipline does help them keep a better appearance over time).
Assuming they are typed correctly, then the couple of INFJs I know are very sexual.
In bed there's a definite openness to explore and try new things with a clear preference for the submissive, though not completely loose - rather contained within a framework of what they view as dignified. When confident there's an attitude of almost playful arrogance that views the self as a prize - "come and get me if you can, I am not easily impressed".
There's a strong open willingness for sex, at least I haven't seen it used by one as a weapon or trade. There is a guiding honesty in regards to orgasms, though not so much in regards to dislikes (sometimes not telling you when they don't like something and just waiting for you to figure it out). With the one I've known intimately we would both often get off to each other's orgasms - It didn't matter who would reach it first - which might be common for men but I don't think it is as common for women as it was for her.
On a side note:
Having experienced sexual trauma in my childhood, I found relations with her... healing.
I think "sexy" is completely subjective. You know, in the eye of the beholder kind of thing.
A student said to his master: "You teach me fighting, but you talk about peace. How do you reconcile the two?" The master replied: "It is better to be a warrior in a garden than to be a gardener in a war." - unknown/Chinese