Getting gold is not as straight forward as you make it sound. My group has like rank 100 in Stormstout brewery and we did it in 16mins, we didnt use any invis pots and our tactic for the last boss was just awful so yes we could probably get gold. That said the fastest group in the world did it in 11 mins and 6 secs while the 11th fastest group was just 18 seconds away from not getting gold, these challenge modes are really really hard and you cant deny that.