You should have taken your uchi to +10 in Sen's Fortress, which ought to have been pretty easy. In fact, you could have done that as early as Blighttown if you're okay with some grinding.
Anyway, the advantage of dexterity builds is damage output against attack speed and stamina consumption. Blow-for-blow, strength weapons will outdamage dexterity weapons by far, but dexterity weapons can more easily chain attacks and still have stamina to do other things. A strength weapon, however, will break an enemy's poise much more easily, allowing follow-up attacks to completely wreck them.
Dexterity weapons are also lighter. One of the lightest "strength" weapons is the zweihander, which weighs in at 10 units of weight. There's a small selection of axes, too, but even the battleaxe is 5 units of weight and you're probably better off with a claymore or bastard sword if you have at least 10 dexterity. The relevance of all this is that dexterity builds, using lighter equipment in their hands, have more leeway to use heavier armours without passing the equipment load break points. Essentially, dexterity builds both move and attack more quickly on average, as well as having higher damage output over time. Strength builds force enemies to stagger and then punish them further.
It's basically a matter of moderating your fighting against going all-in; a strength build rewards one or two well-judged attacks by providing you with additional "free" attacks due to enemy stagger. A dexterity build, on the other hand, rewards a more mobile and controlled style of fighting. A strength build, despite their lower average poise, is going to more easily walk through a dexterity build's attacks and stagger them during a trade of blows. Simply put, dexterity builds exploit weaknesses and strength builds force weaknesses.