I dont think they should have unlimited range, or be this accurate from across the map. People have started to just sit at their spawn with them smoke bomb jump ontop of their base and shoot shurikens at all the enemies turrets. I think the issue is either unlimited ammo or that the shurikens should have a fall off range, even a crossbow has a range limit.
They are weaker from a range, i can tell you that. And they do do little damage to a turret, therefor you need a lot of them. I'm surprised your complaining about them camping turrets and not about snipers killing turrets.
Also, I feel like assassins sitting still on top of high fences would be begging for either a sniper to knock the off or for a support to put his air strike marker on the bottom of the fence.
