Reb Moshe also held that a tefach of her real hair showing in public was not assur. I don’t think (or hope) women are purposefully displaying a tefach of their real hair in public based on that.
He also acknowledged that he was arguing with the Chasam Sofer, and, based on how R’ Abadi quoted him, it seems he didn’t hold that any hair showing was l’chatchilah.
Unfortunately, many people do intentionally expose a tefach (being makpid on the Chazon Ish shiur, of course), and misapply the heter, which Rav Moshe explicitly says does not allow the tichel to be a tefach from the hairline, since the forehead is already two tefachim wide.
Based on the earlier discussion of Reb Moshe, it appears he only favored wigs over tichels by people who are at risk of not wearing the tichel correctly/fully, as I understand.
Which is most people who wear tichels.
I don’t think most women today are at risk for completely removing their tichels (which is why the Lubavicher Rebbe insisted on shaitels only), but some hair almost always shows.