Did I

up doing a DEX build in Demon's Souls? My uchigatana really does not do that much damage at Sharp +4.
You get a pretty big scaling bump when it changes from +4 to S at +5. Also, what's your current Dex, you get the biggest boost to damage from 20-29, then a slight drop off from 30-49, and pitiful gains after 50. Also one of the benefits of forging without an auxiliary effect is you can enchant it. That means either coating it in either sticky wife stuff (magic damage) or one of the flame resins (fire damage); or buffing it with cursed weapon for 1.5X physical damage, or enchant weapon / light weapon for magic damage.
Another reason the uchi does a little less physical damage than the straight swords is bleed build up, strike them enough times with the weapons and they will begin to "bleed out" and get damage over time for a few seconds, it's like a lesser form of poison. If you cause bleed it will eventually do 180 damage to the enemy.
I didn't like having to mess with buffs so I used a moon, crescent, or blessed weapon a lot of the time. They do quite a bit of damage even without a significant point investment in Magic or Faith, though they are eventually outdamaged by the combo of 30+ STR or DEX investment + an enchantment. You probably just don't have enough points in DEX yet.
Another factor is damage type which is more important in Demon's Souls than in the later Dark Souls. The uchi is slash type damage which is strong against cloth armor and exposed flesh, but weaker against foes with metal armor or natural scales (such as the lizardmen in Stonefang Tunnel). That's what's nice about the crafting trophies, as it gives you the opportunity to build a roster of fully upgraded weapons that are good against a variety of different enemy types.
A popular weapon to moon (add magic damage) is the winged spear as it does piercing damage (good against natural scales and chain mail), it has nice reach and you can attack with it from behind a raised shield. Or since there are no DEX blunt weapons (which does extra damage against heavy armor), you might want to moon a Mirdan hammer.
If you got an extra uchi while bladestone farming then you can even moon that, or go with crescent which shrinks the amount of physical damage and increases the proportion of magic damage (as well as adding MP regen). Another fun weapon to crescent is the thrusting sword estoc (which does piercing damage) which makes for CRAZY high damage ripostes and backstab on armored foes.
Faith doesn't mix very well with a DEX build as all the weapons upgraded with faintstone (blessed) are STR weapons.