One of the problems of balancing adventures like this is intrinsic to how they're designed. You have two options when balancing an adventure like this:

1. Make the route of the masks follow one of few pre-designated paths every single time which have been verified to be achievable gold paths with good movement. or
   1. Reduce the amount of masks required or increase the timer to make sure even bad-RNG runs are possible.

Option 1 might sound like a good idea, but it's not as easy to do and leads to boring gameplay. It awards players for "memorizing" the paths instead of figuring out how best to move through the adventure. Players would ultimately just look up a youtube video and reset until they get the "good path". Anet has already increased the timer because they acknowledged the adventure was too hard. But right now the adventure is in a good place and from my experience the chance of you getting a possible run is higher than 75%. Yes it's still RNG but it's the only way to make sure the adventure isn't too easy on average.

How long you've spent on the adventure? Do you have all the masteries? Some adventures weren't designed to be possible to get gold without the relevant masteries (speed boost mushrooms and some lean gliding to some extent). Because I can guarantee your math isn't right and basically just misinformation.