Absolutely false analogy. Boys and girls wear different clothes all time time.
We are talking about special clothes, special garb, a costume if you will. Altar servers have always worn cassocks and surplices or albs or whatever in a a particular parish. To cloth the boys and girls in different garb at a particular parish has no reason other that to make a statement that the girls are just there because they have to be allowed, but we don’t have to let them dress and look like altar servers.
The argument that boys and girls normally don’t dress the same isn’t applicable here, since boys and girls never wear cassocks or albs on the street, either. It’s special garb for Mass, and to separately dress the sexes that are doing the same thing serves no purpose.