I disagree, it’s still useful to 2-handed-weapon users – it’s just that they can only have the shield up after attacking every other round, as opposed to every round as before the change or with your suggestion. It also enables an archer to draw both a melee weapon and a shield and still attack, use an ability, or move during a single turn.
Starting with a 2h, lets say the enemy closes in, my turn. If I hit with the 2h I can switch to the shield after(6+2). But my next turn I will be able only switch back to 2h and hit(2+6). Not being able to switch back to the shield. That makes you shielded every other round if for some insane reason you decide to cycle through.
You get up to +20 to defense (depending on shield) every other turn. The only things you lose by leaving your weapon hand empty at the end of your turn as a two-handed-weapon user are potential damage against any enemies that try to leave your zone-of-control and the ability to move one step before performing a two-handed-weapon attack on your next turn, but if needed, you’re still able to draw an one-handed weapon, move one step and attack. I don’t see the problem.
That is a walid point up till you can fire 4 xbow in 2 turns. To reload an xbow you still need 7 points. So after the first barrage you will need 4 rounds to reload all and be able to shot again. You will not do that. No one will. It is way simplier to fight with only one after the initial shots.
Quick Hands gives you the option to spend any turns where you don’t have an opportunity for a good shot reloading a spare crossbow instead, as I wrote, allowing you to potentially fire two times rather than once when you do have the opportunity. Situational, but it is another reason why it might be useful for a ranged character.