While there is no substitute for "total immersion," people outside of that experience are nevertheless capable of having a drive (whether through a female identity or an intense interest for other reasons) to have an understanding of womanhood, an understanding that possesses its own set of weaknesses and strengths. The "bio girl" experience is also not universal, as not all of them have had babies, have undergone puberty (not surprising for the ones still under the age of 10), or have been treated in the same ways both good and bad (coming from religion, social class, location, the individuals in their lives, and good ol' chance), so cis-women can have the false idea than other cis-women are going to be able to necessarily relate to their own experiences (and this same principle applies to any other demographic... TGs aren't immune, either). There is going to be a great correlation between understanding womanhood and being a cis-woman, but correlation is not an absolute -- and you're the sort of person outside of the cis-female group who is going to be much more aware than the average about what it means to be a woman, and I bet in some (maybe many) ways you know more about womanhood than the average woman.
If a cis-woman basically "pulls rank" and refuses to explain in any educational detail where her perspective is coming from, then she can go suck an egg. If you can extract a more substantial conversation with a back-and-forth, then a greater understanding is possible, maybe where each of you can teach the other a few things (you offering your earnest and insightful observations even while not able to fully participate, while she may illuminate certain nuances you have been unable to see for yourself). The key is that it isn't supposed to be a competition, but rather an opportunity to gain understanding. If the person you are talking to has merit, then trying to engage them to really discuss things should give better results. If they just boast, they're probably too proud or insecure (some can't handle being "out-womaned" by someone who isn't a cis-woman) to be worth your time.