In such a small, intimate area, LoS and other geometry concerns are valid, but I can assure you that we are adjusting the LoS blockers and general terrain on these on a daily basis to make sure we get them juuuuust right for all parties involved, not just melee and ranged DPS. Sometimes there is just too much LoS for the healers and they can't get off their support abilities because their friendly targets are weaving their way through all the blockers. Point being, it is a balancing act and we are iterating on it every day!
I'm writing up a blog post today (it won't be posted until next week or possibly the week after, gotta translate it and get the big bosses to rubber stamp it) to explain in more detail these Warzone Arenas and our methodology in balancing them. Really looking forward to yall getting your hands on them asap! The feedback from players that have played them already has been overwhelmingly positive!
But does the GCD misfire still exist? I imagine it can be pretty frustrating to lose a match due to this bug where every ability counts.