the bottom line to recap, and the main reason I am saying this, is because every single attribute of femininity, is not only present in ponies, it is also present to a greater degree
Masculinity means being large, being dominating in size, having strong and hard muscles wrapped tightly by your skin, with low body fat, it means being a protector, an active agent, a force to be reckoned with, a man is an astute planner, and is solid enough to overcome conflict with other men, those things are the essence of masculinity, the less a man matches with those values, the less of a man he is
Feminity on the other hand, is ideally something that is there to support the men, which is why women are so hated, most of them are selfish individuals, who will never view themselves as part of a couple, but always themselves, and every man she knows as something foreign she can interract with, manipulate, gets what she wants from, etc, that is of course absolutely terrible, and does mean most women completely fail at being women
Feminity comes with a lot of other things, "feminine traits" means "softer traits", even their faces are more rounded, while men have angular everything, angular bodies, and angular faces. Women are supposed to have curves all over their body, be petite, a small and cute little thing that is faithful to the man, and that the man protects, and therefore also provides morale and emotional support, hence the cuddles, hence the cute and beautiful appearance to look at.
And same as with the men, the more a woman strays from that ideal, the less of a woman she is.