All of the mechanics in the dungeons are fairly simple. You don't have hard overlaps and you have some mobs that just need to be interrupted, isolated or kited. The timer makes it hard because you need to pull bigger groups on higher keys to keep up with the throughput required as well as manage spikes of damage that can become lethal at those levels. Removing the timer makes it nearly trivial.
I have a feeling you misinterpreted what I wrote.