I am pretty sure that there weren't more than a handful of players in the realm back then...
When a realm like the one space built is full or almost full, it really makes things harder.. Now, I will not say that it always makes it impossible to pass but lag does indeed make some things harder, if not even impossible (see the case of the weird lever).
I bet you really spent a whole day testing the parkour.. You see, most do not have that time or would rather do something more productive with it. After 20-40 failed attempts of passing something you get confused and upset because people have already finished and you cant.
Being a "tester" cannot duplicate the mess that comes with the public launch of a thing.
I think when things simmer down it will get easier. I can tell you when I first went there the first part without question WAS BROKEN. The outline blocks were not relaying correctly and there was ZERO chance unless you had speed demon three plus jumpman. It resolved itself out though but was a nightmare in the beginning.
lava jump in ice, without any perks at all you would find yourself dying after 3 ticks, each lava hit would be 1.5 damage. on a qbee with 3 hearts, 2 ticks, in which is impossible to pass 5 blocks unless glitched, but hard to pull off if you were to try (infinity jumps)