The average DRK can be countered but once you actually get a team that can cover it like... a Paladin which is also one of the roughest class to deal with then good luck. This is not even complaning since it's not common to find and it is much harder to pull if you do not have premades but there you go, a Dancer can be easily shutdown since the Charmed effect isn't instant like Reaper's Hysteria so you need a tank\healer to make sure it doesn't get nuked.
Regardless all 4 tanks are deadly in FL, you have 2 who have 10 sec invulnerability (Paladin and Dark Knight), 1 that removes guard, can't be CC under LB aside Imp and lower your damage with Orogeny and 1 that has a fast LB regeneration and can wipe full groups if not focused (Gunbreaker) with a buffed LB and a buffed Nebula.

Straight up it's Frontline, there should be a proper balance and not just stat wise like the horrendous damage reduction, there has to be a check on how some abilities behave etc.

I mostly post this because i still enjoy Frontline and there is plenty of times i had a blast but sometimes i wonder how the game would look if the mode was properly mantained. It took so long to finally get rid of the interaction Guardian Cover but still Paladin is a monster in stalling\defending and makes other classes' play much easier and harder to counter as an example. Ninja remains king in tanky ranged harassment and can just sit back and not worry on over committing and just be ready to LB from afar and even if it is on melee range, it can easily tank and escape. I thought before 6.1 dragoon would be annoying to fight, i was not ready for this lol