Not true. I've been with women who loved fisting and it's actually all about muscle control and has nothing to actually do with "stretching." As soon as I would pull a fit out, both were able to simply tighten back up on my cock. I'm big tho, 8" and fat, but still, they both had amazing muscle control.
I have a serious fetish for women who love big toys after being with a few women who loved fisting. They adored and craved the extremely full feeling and that lead to both experiencing squirting on a regular basis.