one handed weapon and sheild - overall adds +1 to AC

two handed weapon - generally increases the damage die by one level adding +1 to damage on average

So what about for two-weapon fighting if we have

two-weapon fighting - add +1 to attack roll

My question is this: From a math point of view this has a lot of symmetry to it. You can choose if you want a buff to hit, damage or defense and all the buffs are about equal. However from a role playing point of view I think the +1 to attack roll misses the point of having two weapons i.e. you should get two attacks somehow. I mean, you can justify it. If you are swinging two swords at a guy then there has to be a better chance that one of them will connect. Its not a very satisfactory explanation though.

So is the symmetry of the math enough to overcome the kind of arbitrary and unintuitive nature of the bonus?