Vaginas are stretchy and will go back to the way they are after sex, UNLESS you're fucking something that is beyond the girth of your vagina. If your vagina is GENETICALLY narrow and you fuck a toy that is as thick as a baseball bat you are gonna stretch yourself out beyond the elasticity of the vagina. You will feel looser, but only to men who have baseball bat dicks.
That being said vaginas are normally loose enough so that no normal penis, (excluding giant monster dongs in porn or if you're above average), will ever stretch out a vagina. Vaginas are made to stretch enough to give birth to a baby's head then they go back to normal.
Genetically there are women who feel looser, just like there are men who are bigger and women who are narrower. It's not loose because they got fucked by 1000 normal penises. Even if they did get fucked by 1000 normal penises it would not be looser, key word NORMAL.
IF they got fucked by monster toys and things that are thicker than their maximum genetic girth, then yes they'll be looser than before. But the odds that an average woman is a size queen and is testing the penis girth limits of her vagina is slim. Girls like to brag their vaginas are tight, they're not gonna fuck monster dongs and stretch their vag's out unless they're size queens.
Unless you're penis is thicker than a baby's head, you're not gonna think a vagina is tight unless you're fucking her and she's dry as fuck. Vagina is always gonna feel looser than your hands.
TL:DR Both of you were right, to an extent. You can stretch a vagina and loosen it, just that normal penises cannot do that. Unless there is a significant size difference between the two people. For example Hafthor (The Mountain) and his wife. Chances are women are not loosening their vaginas fucking even 100 normal penises.
Thank you for coming to my T.E.D. talk.