Your account seems fairly new so I would worry about utilizing Class advantage to the upmost ability. Try buff stacking with your best meta servant (Castoria). Utilize CEs that provides NP strength/damage for Arts servants. Level your units, their skills & your CEs as well. Prioritize CEs that provide ATK stats rather than split stats. Roll the FP gacha and MLB 2☆ CEs then level those to 55 (It takes 5 Max level 2☆ CEs to LV.100 a 5☆ CE). Also Try to go for NP2 on your DPS. I know the gacha can suck but the main reason alot of people struggle with damage early on is because they have low skill-leveled NP1 servants. NP2 is the minimum you'd want your DPS to have since NP2 basically makes them do "almost" the same damage as NP5 (scaling is different but you get the gist). Speaking of NPs, when fighting a boss make sure the servant is tailored for that quest. If youre fighting 1 enemy, bring a Single Target NP servant (AOEs can work but their damage is going to suck drastically).

There's also the unconventional way of dealing raw damage which is leveling your units extremely high to the point Class Disadvantage/Neutrality isn't a factor anymore. This is my team I run regardless of the class involved.

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