We didnt run into any of the rng you are, sounds like you need more dps tbh
People cannot suddenly puke up an extra 2k DPS to take out traps when you have 2 DPS missing. The RNG is ridiculous.
In that video you posted you got luck your healer gets trapped or thrown twice in the third phase thus leaving your DPS out to break traps/kill boss. So basically the RNG was with you.