I have always played yul since Chronicles 2 so here is my advice.
Yuls damage is all about skills. Here are some of the most important upgrades that will improve your damage.
1. Get p.skill power and p.skill critical damage on your bow and cloak
2. Get your dex to a minimum of 90. Dex increases your p.skill rate.
3. All the items you aquire make sure they will increase your skills critical damage, rate and power. Get Aries and cancer for agathions there are also many artifacts that will help with that. Angel ring +6, Paulina R99 ring etc.
4. Enchant your skill with focus until your p.skill crit rate is at least 80%. When you crit just about every shot then you can switch it to break to increase your damage even more.
Increasing your p.atk is also very important but should be secondary to all skills items.
But unlike some bad advice you are receiving... go dex, dex, dex.
I used to have +10 str and +5 dex after going all dex I had quite a noticeable difference as I landed more skill crits resulting in overall much more damage.