To the point... I'm not sure if it's difficulty, as much as it is complexity. Consider all this:
a BLOODY HUGE things starts walking towards the party, the party having to move BACKWARDS - neither is something seen before
the thing keeps walking, forcing the party to do the same, there's NO STOPPING WHATSOEVER (especially if the party also misses chaining it) - again, not something seen before
if you get stomped on, you die, that's in addition to the fact that the thing keeps popping AoEs spanning across the entire width of the platform
adds keep coming in ENDLESS WAVES, and they can't even really be cleared away as usual
objects to INTERACT with along the whole length of the bridge, having to go FROM ONE TO THE NEXT, CONTINUOUSLY, as they keep getting destroyed, AND TARGETING moving mobs - another thing we're not really used to
additional SPECIAL objects to INTERACT with, which aren't even easy to spot if you don't know where they are
all these having to be TIMED over and over again, WHILE of course MANAGING all the mobs AND DODGING all the AoEs
So yeah. I think it's easy to see how and why all this would overwhelm people, especially when (nearly) everyone's new to the duty and does not even know the layout of the place itself. Even more so, when this is not what the average (casual?) player, who doesn't do current endgame raids, is used to.
It just seems like the devs had a thought and went all-out, stuffing all kinds of mechanics they could think of into this one trial, for - whatever reason. It's very far from what we had been trained for up until this point. And once again, they stuck an i90 requirement to it, with abysmal tome rewards and no loot drops at all (even though the complexity would warrant it, imo), so overzealous (hardcore?) people are free to ragequit after one wipe. Sorta baffling and unfortunate, in my opinion.