The benefit is that you are able to kill two goblins in a round, instead of one. When you face 10 goblins and a goblin shaman, being able to cut through the mooks in 5 rounds instead of 10 is a benefit.
...
With this configuration, 1h+shield gives you better armor. 2h gives you better single target damage. And TWF gives you better multiple target damage. I think it's a good solution.
I am quite a lot fine with this.
TWF is a fantasy cliché with very little to do with historical realism, so I'm fine with the fact that
a 1st level character is not supposed to get much out of dual-wielding. I am quite sure that this first feat is only the "entry cost" of the style and will be followed with other feats that will make TWF more interesting
at higher level.
Dual-wielding (in reality) is damn hard and requires years of training. In fact, it was a non-existent style in regular warfare, and probably studied only by a few elite duelists. I think it is only a good thing if the learning curve in D&D is also steep... I hate seeing low-level characters effectively picking up a style that should be for the experienced heroes, just like I would hate to see a low-level wizard flying and teleporting just because it's a fantasy cliché.
Also, while I think that historically (at least in the western fencing and swordfighting*) the second-hand weapon was used mostly for defense, you cannot seriously believe that a dagger or sword can effectively protect you from projectile weapons like arrows... it's just isn't possible. That general +1 AC would be a very generous gift if it didn't cost a feat. Of course, it's a
fantasy game, but my rationale is that there has to be a sort of
progression of the fantasy elements, so that deflecting arrows with a dagger becomes possible at mid-levels.
(*Eastern martial arts have
some dual-wielding techniques, for instance the use of 2 Sai or 2 esgrima sticks, but always with very light weapons that are usually more meant like an "upgrade" or extension of your unarmed attacks)
There are two approaches for something like this: design feat chains or use level prerequisites. 3ed established a sort of mantra that straigh level should not be used as a prerequisite (why?). I say that straight level works great, because a gaming group can so easily house rule that so that if they want a more superheroes game where 1lv PCs can do all the fancy stuff, they can just remove or lower such prerequisite level, while groups who want the game to stay more grim-n-gritty can increase e.g. all feat prerequisite levels by a fixed amount.