„My last partner wasn't stimulated by outside pleasure at all. Both fingering and licking did nothing for her. Instead she felt insertions really intense.
That was totally different from my prior experiences, where outside stimulation was essential, especially for orgasms.
Is such a diverse reaction common? Could the cause for this be a more covered clitoris, a more inward shape or maybe just a low concentration of nerves?
In that regard.. can the sensitivity be trained? Is that a topic in tantra?
There may be many reasons for this, including psychological (social/family upbringing, cultural perception, childhood/youth trauma, etc.).
Normally, external female genital parts are susceptible to stimulation and are essential to achieving an orgasm, especially the entire clitoris area, which isn't just a 'tip under the hood', its parts (bulbs) also hug the entire area around vagina and are hidden under the skin of outer lips (Labia majora)
It doesn't change the fact, however, that sexual pleasure is diverse and isn't about just an orgasm alone.
Anyway, I would recommend trying less intensive and focused stimulation, especially when your partner doesn't react to such a direct stimulation positively. Take your time, like you have all the eternity for this one session.
Instead of just going straight to the licking of clitoris glans/tip as soon as you can, try first to gently massage inner thigh area and pubic area without stimulating the vulva directly, then continue with a prolonged and gentle massage along the entire area around outer lips bottom to top, and only then, when you feel the positive feedback, it's time to include the clitoris glans to the play.