So I moaned about the inherent unfairness of a DF Scout with Heroic Archer, under a Missile Shield and Dark Vision spell, versus normal ranged attackers. This sparked a discussion about multiple shooting with bows.
Mark Langsdorf seemed to suggest dumping Dual-Weapon Attack as an option, using Rapid Strike only, and using the rapid fire rules to treat them as one attack dealt with through one defense instead of multiple attacks versus multiple defenses.
William Knowles pointed out that it's not reasonable or realistic for a person to shoot two arrows at once at full power.
I don't think that's the issue, though, because GURPS assumes you can, indeed, attack twice at full power in a turn if you attack with two weapons (Dual-Weapon Attack) or one weapon (Rapid Strike, All-Out Attack). A Heroic Archer could use Dual-Weapon Attack to shoot two arrows at once, but equally one can shoot one arrow after another at a net -1 for two shots by using Rapid Strike. The base -6 to hit on each is halves to -3, then halved and rounded down again to -1 if the Scout has Weapon Master. So even if you hit Dual-Weapon Attack with the nerf bat, Rapid Strike is left alone. And melee attacks, no matter how many you use, don't use the Rapid Fire rules (which make it less likely you'll land both, and lets the defender avoid them with one defense.) And I think if you hit that with the nerf bat, you have to do it to melee attackers too.
None of which seems very high-powered cinematic dungeon-bashing game to me.
In my experience, though, the problem isn't two arrows into one target for a -1 to defend against both. That happens, though, and it's not an issue of Block at net -1 plus Block at -6, but Block at -1 and Dodge at -1. Generally, though, the Scout tends to shoot two different targets ("Those two guys, vitals.")
But I do think it's fair to give a little something to people who get shot with two arrows at the same time.
Right now, you can reduce the penalty to stop each half of a two-weapon attack with the (cinematic) Dual-Weapon Defense* technique (Martial Arts p. 83). Some two-handed weapons can parry both halves of a Dual-Weapon Attack at a total -1 (Parrying with Two-Handed Weapons, Martial Arts p. 123)
So here is an optional way to deal with this with shields - a combat option and a technique to buy it up.
Add the following line to Dual-Weapon Defense*:
"You can also learn Dual-Weapon Defense for use with a medium or large shield. This lets you buy off the -1 to block both halves of a Dual-Weapon Attack, with a single block."
Then add this to Multiple Blocks:
"Dual-Weapon Blocking: With a medium or large shield, you can attempt to block both halves of a Dual-Weapon Attack with a single block. Success wards off the two attacks. On any failure, though, both blows hit!"
You can limit this to large shields only, if you prefer - I went with Medium to avoid turning Large Shields in the only truly useful shield. The nice thing is anyone can try this, cinematic technique or not - they just can't improve it. This takes a good step in the direction of making shields the ideal defense against a storm of arrows instead of just your first choice before you drop back to Dodge.
I think it's fair, really - bowmen, even Heroic Archers, have to have a higher skill for the same effect as a melee combatant, do lower damage, have a more limited ability to lower defenses (Prediction Shot, not full Deceptive Attack), and need a magic item (Cornucopia quivers) to avoid ammunition issues. The above simply gives a little something back to shield-using foes getting pinged by multiple arrow shots.