My 9yo is very sensory and I ended up following his lead on clothes many, many years ago. At 2.5 his preferences began to emerge.
Because he is particular, we do often end up with "girls" items. There is much less choice in soft, fluffy "boys" items, and if he needs shorts from September-April, he does sometimes end up with the "girls" cut. He's not in dresses, pink or sparkles, but there are sometimes a pink trim such as a zip or stitching. Sometimes shoulder length hair perplexes people, but then if he was a girl with the same style that wouldn't be feminine and long either 
Anatomically, there should be no difference in cut for childrens clothes for about age 10 and under, and there wasn't in the more androgenous 80s and 90s, but many "girls" clothes are cut tighter and shorter so I can't begrudge a girl finding "boys" clothes more comfortabe than "girls"
Clothes should be comfortable, and a child should have a selection avaliable for a range of occasions. Sports clothes are fine for school parties/ activity parties. Some smarter, loose cut trousers and shirts might be better for more smart occasions. In the absence of very formal occasions "boys" clothes rarely go more formal than that.
I don't blame girls that prefer the more practical, relaxed cut of "boys" clothes. Many women do need a "women's" cut due to body shape, but there are many women who wear more unisex items and rarely wear clothing that is "feminine" (skirts, dresses, tights...)