They balance themselves into hell, if they try to make arenamode skills work in frontline.
They could make seperate traits/skillsets for each mode, but their PvP agenda is casual-orientated, so they wont add too much complexity to it.

Something as simple as making heals cost 5k MP instead of only 2,5k in frontline and let sprint have a cooldown while in combat, would make it more PvP focused, as you don't have an easy way to escape.

Paladin hallowed ground could be changed to shield with 150% of his maxHP when used, making it useless in frontline when ganged up upon, while keeping much of it's efficiency in the arena mode.