Not necessarily. While a mature male will frequently have longer, skinnier legs (and a smaller abdomen) than a female, I don't believe that becomes apparent until they are much closer to maturity. With slings, they all look very much the same. Even variations in abdomen size with slings is more likely to be due to eating habits (how much, how recently) than with sex.
Pamphobeteus/Xenesthis/Theraphosa spp. and even Grammostola iheringi are all leggy as slings (examples below), freshly moulted tarantulas appear leggier/skinnier than those that haven't moulted in a while.
Tbh, "it's leggy/skinny" just isn't a good way to tell the sex. Vent sexing/moult sexing are far more reliable.