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.
No...fighting with a dagger in the off hand is not that hard...at all. It's no harder than fighting with a buckler in the off hand, and the purpose is the same. It can be picked up in the same time it takes to get basic familiarity with a rapier, ie a few months. The masters taught rapier and dagger, rapier and cloak, buckler. The idea was to have an object in the off-hand to help block, because early rapiers were really long, really heavy, and could only fence in single time. As rapiers lightened, becoming smallswords, the ability to fight in double time (parry
and riposte) became easier, and an open hand to grapple with became much more common; except for the Italians, who loved them some daggers.
In reality, two weapon fighting is not the outlier, single weapon fighting is. You fight with your whole body. If you're wielding a one handed object, you either grab and punch with the off hand, or grab your weapon in two hand to hit harder. If you've got access to a second weapon, you pull that out to block with, or stab with. And don't forget to kick, bite, headbutt, pommel smash, swing the quillons into their temple. If you're using a buckler, you grind it into your opponents face as you cut at their legs or stab them in the belly.
It is true that the Master's tended to consider fighting with two swords to be very difficult and not something to try until you'd mastered using one sword in either hand. Based on my experience, it's not that difficult, but tends to have the disadvantage of causing you to face your entire body towards an opponent. When fighting with two swords, one sword should always be primary, the other used opportunistically. The advantage of rapier and dagger is that this comes naturally (the rapier is always primary).