Except TES V: Skyrim is an RPG. It doesn't make sense for every playstyle to be viable when the player is supposed to be role-playing a playstyle that he or she genuinely likes.
If you wanted to play sword/shield for the months leading up to the release of Skyrim, but found out that dual wielding two weapons is a far better option, would you really change your mind? Are you really that shallow? Actually, that doesn't even matter, because regardless of whether you choose sword/shield (because that's what you genuinely wanted to be) or dual sword (because you simply cannot help yourself), you're still doing it right. You're still playing the game how you wish to play it.
First of all, I'm not shallow :sadvaultboy:
Second of all, there's been balance in every ES game, to some extent. In Oblivion claymores are more powerful than longswords, have more reach, but are slower. Longswords leave you less encumbered, are faster, but deal less damage with less reach. Using a shield makes you more encumbered, but gives you better blocking. Daggers have lower reach and damage, but are MUCH faster.
Now in Skyrim, Duel wield will be faster, and deal a large amount of damage, but will have few defensive capabilities. Claymores will have more reach, are slower, deal equivalent damage, and have better STATIONARY defensive capabilities (you won't be able to dodge as easily). Longswords will be faster than claymores, but deal less damage with less reach, while having better defensive capabilities. Adding a shield will make you slower, but give you even more defensive capabilities. Daggers are faster, but deal less damage with fewer defensive capabilities, but deal HEAVY damage if used from stealth.
The system works well. All of them are balanced, while staying true to their core mechanics. You can dodge and avoid enemies with duel wield. So if you play it cautiously and think on your feet, you'll be untouchable and be able to tear people apart.
I'm probably using Duel-Wield as well as Archery on my first character. Just because it can't block doesn't deter me. It sounds like it DOES deter you, though.
Edit: To the part you added after I quoted: No, balance is to keep the game working so that every playstyle is enjoyable and can compete with the others. People playing on Very Hard don't want to get trashed by a bandit with duel-wield, just because the player wanted to use a single sword. If they die when balance is implemented, it isn't because Bethesda made on playstyle superior.
Just because you don't get deterred because something is weaker, you automatically condemn those who want balance as idiot who can't choose their playstyle, not as people who want the game to be based on skill with their playstyle.