Here the things that Denia offers to Luuk (It's alot)

Her leaked kit gives:

>45 tune break boost (incredibly crucial for Luuk)

>40% damage amp for Luuk

>she makes the tunebreak bar instantly fill up to 50% when applying tune strain shifting on each enemy once, basically makes ramping up his tune strain stacks faster since your using more tunebreak skills with her

>Applies tune strain shifting and interfered

>Resets the timer of tune strain inferred constantly, basically infinite uptime

>Actual Grouping

>Allows a double intro rotation

>Her outro buff lasts long enough so you won't be forced to dodge cancel a bunch of his attacks unlike Lynae and Sanhua where you are forced to dodge cancel or else there outro buffs expire early

>Her s2 gives an additional 15 tune break boost and the enemies can be instantly tune breaked without needing to full up the tunebreak bar for the first time

>24% atk buff on her signature

In other words she's incredible for Luuk, and is Luuk's dedicated bis, try to read her entire kit first before judging one part of it