Well watching the video I can say I'm 100% sure your build is bad. You're not using this weapons the way they are designed to be used and is not using the correct resources to increase their damage input. Looking to Relanna she doesn't look particularly challenging to me.  Look how your clone is using the Moonveil more efficiently than you making use of its broken Ashe of War

If this is the playstyle you want, dump Moonveil and dual wield Uchigatanas and change them to occult infusion, respect to Arcane and watch this build decimate bosses (literally beat Malenia first try)

(Sadly don't work in bosses with bleed resistance like Radagon and Elden Best)

Were you not even at 50 vigor? I'm curious, how did your build looks like? 

Rule of thumb: 50 to 60 vigor ALWAYS. Forget about being a glass cannon, it's not worth it. If you still not feeling 60 vigor is enough try Morgotts Rune. Otherwise use defensive talismans

Survivability comes before damage. There are too many flasks and recover options to save your ass if you know how to recover in the right moment. In practice you have very good health options to kill bosses slowly in attrition battles. It's safer than going for higher damage but getting killed quickly before getting the opportunity to use flasks to recover 

50 endurance is way too much unless you're using strength builds with very heavy greatweapons, in any case if you are one-handing a strength weapon don't go past 54 strength, single handing gives you a 50% boost in str and the soft cap past 80 strength makes the returns minimal 

Don't wield great weapon if you main stat is not strength, this kind of weapon needs big endurance investment which imo is not worth it 

If you're not doing strength build, use whatever endurance you need to equip a good armor (target 51 poise), wield your weapon(s) and still mid-rolling 

Never go over 80 in your main damage stat. 70 can work. If you weapons scale with two stats sometimes 60-60 works better than 80-40, you need to see how is your weapon scalling and decide which attributes makes sense to raise 

Instead of upgrading endurance and other damage stats, see if you have enough faith to use a sacred seal and use buffs.  The boost in defense and damage done is often bigger than what you could get investing directly in stats damage or investing in endurance to use heavier Armour (clawmark seal only needs 10 FAI)

I'll try that indeed, I didn't know there was two uchigatanas. I'll have to find the second one before I can respec to Arcane. What exactly is occult infusion, I haven't played Elden Ring in a while, I know I infused bleed onto the uguchigatana but I'm not sure how the mechanic goes. 

You can only get two Uchigatanas in NG if you started as Samurai. The Uchigatana is a catacomb in Northern Limgrave

Occult Infusion makes your weapon getting scaling with Arcane and increase stats buildup such as bleeding and poison. There are few Ashes of war with occult scaling. The best way to give a weapon occult affinity is using the black whetblade, you can find it in Nokron

It's worse than bleeding infusion when it comes to proccing bleed, but it's add strong arcane scaling so thr damage output is high without compromising your ability to make bosses bleed 

At 80 ARC it's only marginally weaker than Keen Uchigatana with 80 DEX, but with much higher bleed buildup: 

11STR 15DEX **80ARC**:  

Occult Uchigatana = 585AR / 88 Bleed  

11STR **80DEX** 8ARC:    

Keen Uchigatana = 596AR / 45 Bleed

Combined this with Mimic tear and most bosses will bleed in every combo

However be aware some bosses are immune to bleeding, many of them actually. If you don't have many Larval Tears you can go for DEX and change the affinity to Lightning, Keen and Blood Infusions whenever you see fit 

If you really to keep INT and be a magic Samurai I strongly advice to use ranged magic and abuse Moonveil's Ashes of War. Intelligence builds are great, but a good spell blade build is about mid-range fights (using Cold, Ashes of war and some ranged sorceries) and your playstyle looked 100% meele for me 

If you want to meele IMO DEX, ARC and STR are better stats than INT

You can only get two Uchigatanas in NG if you started as Samurai. The Uchigatana is a catacomb in Northern Limgrave

Occult Infusion makes your weapon getting scaling with Arcane and increase stats buildup such as bleeding and poison. There are few Ashes of war with occult scaling. The best way to give a weapon occult affinity is using the black whetblade, you can find it in Nokron

It's worse than bleeding infusion when it comes to proccing bleed, but it's add strong arcane scaling so thr damage output is high without compromising your ability to make bosses bleed 

At 80 ARC it's only marginally weaker than Keen Uchigatana with 80 DEX, but with much higher bleed buildup: 

11STR 15DEX **80ARC**:  

Occult Uchigatana = 585AR / 88 Bleed  

11STR **80DEX** 8ARC:    

Keen Uchigatana = 596AR / 45 Bleed

Combined this with Mimic tear and most bosses will bleed in every combo

However be aware some bosses are immune to bleeding, many of them actually. If you don't have many Larval Tears you can go for DEX and change the affinity to Lightning, Keen and Blood Infusions whenever you see fit 

If you really to keep INT and be a magic Samurai I strongly advice to use ranged magic and abuse Moonveil's Ashes of War. Intelligence builds are great, but a good spell blade build is about mid-range fights (using Cold, Ashes of war and some ranged sorceries) and your playstyle looked 100% meele for me 

If you want to meele IMO DEX, ARC and STR are better stats than INT