I have noticed some of those as well and they are stupid as fuck. The greater rifts while interesting on one hand you can try and measure your e-peen with them and on the other hand there sure is a fair bit of RNG to them as well. The long ass hallways as you mentioned are one since if you die you are running back for minutes vs. a rift where you dive deeper and deeper into the short levels where you can respawn close by. Another issue with mob density, while I couldn't care less about it during Rifts in Greater Rifts it can be frustrating when you run into long stretches of little to no mobs since you are so pressed for time. Then the last bit of RNG and the part I mind the least is you can get fucked on the type of mob spawns. You can get those gay ass Arch-angel faggots charging your face from off the screen or you can get easy as fuck zombies. It's still fun to try and clear higher and higher rifts but it can be frustrating when you know the only reason you didn't beat the timer is due to one or more of these reasons.
As for those asking about gearing up for Wizard's finishing the Firebird's set always going to be the first priority then it will be gearing out the other slots with specific items that will help push dps and fire damage higher. Then you just hope you get lucky with those end game pieces. I have yet to find a Furnace, Serpents Sparkler, Witching Hour, Unity, Cannot die followers token. Even so I am still holding my own so while I really am hoping to find those pieces that will allow me to compete in the top ranks of the season I am also not planning on killing myself farming 1% drop rate items or bitching about them. With as easy as they made everything else in this game there should be at least a couple of carrots entice you.