I agree with your theory. Men and boys tease each other amongst friend groups as well. The reason they do this is exactly the same as your proposal about why they'd do it with the women and girls in their life - to help each other build a thicker skin. Being teased in a safe environment, and learning how to deal with it, means that they are able to deal with when teased or verbally attacked in an unsafe environment. It allows them to learn how to deal with negative emotions, like you'd pointed out.

Women and girls are much less likely to do this in their friendship groups. Instead, they are 'nice' to each other (even fake 'nice'). When they verbally attack each other they usually are doing it to actually attack each other, rather than to help the person being teased by strengthening them.

It is very likely that this male behavior is beneficial to women and girls as well, when men do this with the females who they are close to.

The loss of this dynamic is partly to do with feminist discourse that entirely misunderstands this aspect of male interpersonal communication. Feminists see men teasing each other as men "not having proper friendships" or "men treating their friends badly". They are unable to see that male teasing is actually a sign of a strong friendship, that men do it with each other to help each other. They also don't see that men use it carefully - like you've pointed out - men are perfectly capable of using their empathy of determining when they might have overdone it and pulling back, and most do so. (It is true that men tend to dislike other men that are unable to take any teasing and always over-react, but there are good reasons for that as well). This means that feminists discourse encourages men to stop doing this and instead be 'nice' to each other, to the detriment of both men and women.