it's a myth. I was told the same thing at a very young age and I know many many bigger-breasted women who have extremely sensitive nipples (or at least they've told me so).
My view derives from numerous personal observations. The smallest breasts I've ever known (she still weighs only 90 lbs) could also achieve orgasm with careful play.... I've experienced wonderful large breasts with sizable, sensitive nipples, which is great. But a lot of Ds and DDs have huge aureoles with very tiny nipples, and I just don't enjoy that as much. Of course, these things are like window dressing in a way. I've fallen deeply in love with women of all shapes....
There does seem to be one particular kind of large breast that has a sand dollar sized areolae and a disappointing nipple. But the biggest nipple I ever sucked was on an accountant with at least a d cup. I wouldn't tee my golf ball off those not even for a driver.
Being an ass man myself, breast are a great bonus on the package and I like all kinds.
I've enjoyed breast small enough I could get most of one inside my mouth. And I've laid my head between a set that closed in around my ears. Both extremes and all those inbetween have advantages and disadvantages so I just love em all.