If i am correct,
a 2h Weapon class(2h spear,musket,bow) or using 2 weapons(sword and dagger/pistol)
will be able to use shield while still be able to cast all their 2hand or 2weapons skills
For Example: in Team Battle League i saw a Lancer build(2h spear) using shield when but hes attacking he is using 2h spear with all 2h skills.
Also a Assasin using Sword & Dagger but when somebody attacks him, it is very low damage because of shield equipped in weapon swap slot.
i think this gives a very unfair advantage to them making some classes very overpowered and highly unbalanced.