We've never once seen any man struggle to hold a woman, but we've seen many instances of women being unable to shield men. It's intuitively obvious that opposite sex shielding is more difficult in general and that shielding requires quite a bit of power in general. I'm attempting to theorize on WHY this is the case.

It seems to me that part of this reason is because of the nature of the relationship with the OP and each sex. A shield for a man would need to be constructed in a way that would allow for the very aggressive flow of saidin, while a shield for a woman would need to be more flexible to allow for the more immersive flow of saidar.

In theory a shield woven for a woman and placed on a man would tear/rip apart quickly because it's not rigid enough to absorb the velocity of saidin coming at it (assuming strength is in the proper range for a man to be able to break a woman's shield etc). Just as a rigid shield designed to hold a man would shatter rather easily from the mass of saidar coming at it.

Naturally overall strength will make an impact, but I think this is why a woman can easily be held by a weaker woman and to be honest I believe it's easier for a man to shield a woman than it is for a woman to shield a man. I also believe it is easier for a man to shield a man but overall I think it's just harder to shield a man in general

man shielding woman < woman shielding woman < man shielding man < woman shielding man