They are, they're just not that relevant outside the US. Plus their songs are kinda forgotten.
Still, they're real legends unlike, let's say, Janet.
Diana was local I agree, but Tina had a cute little moment in Europe for some time. And Simply The Best is used in commercials all the time (I don't think people Tina sung it though).
No, she definitely is.
She has the success, the iconic moments, accolades and industry respect, talent, but most importantly musical influence.
Cyndi has influenced just about every major pop girl today, even Nicki lists her as an influence. You'll be hard pressed to find a female popstar who doesn't list her as an influence.
Not to mention everyone knows Cyndi Lauper, plus all her LGBT work.
Nothing says she isn't a legend, I mean she's a musical pioneer tbh.