I have Li+9 and I use her mainly for wars for the mana cut, so I only benefit from increased stats.
I thought the costumed Li could be good for some 4* tournaments but I can put better (faster) rogues on wings. And in the last Bloody Battle one I decided to use the regular one for the bigger mana cut again.
So I only used costumed version on some tournament battles when I wanted to use holy stack (with Jackal), it was a dodgy duo
In your mono team - are you able to one-shot with Joon+Chao? Would you be able to do with Li (costumed probably)? If yes, then it could be an upgrade to your team (Chao’s mana cut is waisted anyway). You only need to use lvl 5+ mana troop to get her ready with 9 tiles so she can fire with Joon more often.