Hi after watching your video there was no issue with Rogue Val, but with your playstyle, lemme explain.
When you were focusing Sunny, you were just using your autoattacks and Flame breath. Thats not enough dmg at all. You also used Charge from time to time but you missed it MAAAANY times, so again not enough dmg to bring someone down.
The biggest mistake was that you werent using your Rock throw and Leap Smash (almost) at all. Those are your most powerfull abilities and instead of using them , you were just autoattacking and your RT and LS were waiting there ready to be used.
Dont take it as negative critisism, i am just trying to show you what you did wrong.
Next time try to use your Leap Smash+Rock throw combo, as often as possible ( straight when they are out of cool down). If you combine this with good aiming, you will have no problems at all to burst someone down.
Amd back to topic : you should focus Rogue Val first to pop her Healing Burst and then Focus support, and the healing from RV will be nothing .
Good luck practising!
@Mindoci youuu ninja