No it doesn't need to be two way. If you look at Jeanne you can see her statistics even if her back is to you. The way I see it being fair is if you have a better idea of what they are class wise, and you see them use the skills you may see their proficiency with it. Otherwise you'd just see the statistics. If skills are able to be seen without it I believe like you say it makes it a bit to transparent. Likewise it didn't take long in Zero to suss out who was who when compared to Stay/Night.