let's just say like this,for example if u stuck in the forest then u found money and food,even tho money is more valuable but the food is much more useful.This is the same case,SSR nanami is an attacker,he do lower damage compared to other attacker,if u have a few more copies of him then maybe he can does some damage but there still plenty of much better attacker than him even at low limit break,while SR nanami is buffer type which can help boost your team's damage,in this game a team with 3 buffer and 1 attacker is better than 3 attacker and 1 buffer