Both classes can loop their Super Armor and Forward Guards without having any problems in exhausting their evasions/roll.
The only opening we have is to go around the character when they are using forward guarded skills. Or grab them, but other classes does not have grab and some only relies on ranged abilities.
-Increase Cooldown of Void Knight's Nightfall by 1 sec. or reduce Dark Mist i-frame.
-Increase Cooldown of Grandmaster's Knee Hammer by 1 sec. or remove forward guard on Shoulder Thrust's flow: Whirlwind in arena.
- Let every class have the ability to loop their super armors (the same as these 2 classes), leaving only the forward guard skills as the only opening. Although, this will make the pvp experience more like a Black Desert PC version. [but this option will be a lot of work]