From my own point of view, most parties fail this fight due to poor communication.
Literally, I have seen many new players, asking questions but each time getting super vague answers. Let me give you a few examples:
1. "Hey guys, how do you safely dodge the Divebombs? I seem to be ******* up quite a lot and I don't want to keep messing up the fight."
Answer from group: "Just run up and down." This is a typical answer from a random pick up group.
I would tell the new guy: "Hey, during that phase of the fight, the entire group should stack together in one little corner area, just remember to pay attention to what the group is doing. If we all hurdle together, you need to stack in with us. Once the group stacks in, pay attention to a green marker over a random players' head, once that marker appears, you really do have only about 1 second to react to this and run upwards in a straight line along with the group. Remember not to run too far out, because you need to run back and stack within your group again in the same exact spot after Divebomb is dodged, so you can anticipate/prepare to dodge the next one."
See, it takes one simple paragraph, possibly can be typed in less than 2 minutes, to better explain to a new player a specific phase, rather than just being lazy and typing "Just run up and down." or staying absolutely silent.
Most of the time, people expect you to watch a video and know the fight 100%. Again, very kiddish and immature thinking. Some of us older folks really have a lot of trouble with this. Just because we watched a fight on YouTube, it doesn't mean we can own the end game hardcore fights. What you watch in video, is drastically different from what happens in the actual fight. Players may not be using the same strategies as you saw in video, people may not position themselves properly, according to what you saw.
A slight difference in game play, could totally disorient us from performing at our highest capability/efficiency. The real way to get better, is to go in, die a few times with the group, know what each other is capable of, tailor your strategy and then clear it.
It's not impossible to do so with a DF in my opinion. Just need better communication. I don't think hardware or internet connection is the real culprit here.
2. "Hey guys, how do you dodge the Twisters?"
Answer from the group: "Just move." Again, typical response from random DF groups, if you're lucky, you get a sentence out of them.
I would tell the new guy: "During this phase of the fight, it will be similar to the Divebomb phase, you just need to pay closer attention. Remember how the group stacked together to dodge Divebombs? Well, the Twisters requires the same attention focus. You need to pay attention to what the group is doing. When you see people spreading out to the other parts of the room, you must do the same. At this part of the fight, what you want to do is to keep a good distance between you and any other player. Hit Ctrl+F (or Shift+F I forget) on your keyboard, or if you're using a controller, focus target the boss by filtering through targets using your omnidirectional control stick. Once you have focused the boss as your main target, just watch closely as he casts "Twister". When he does, there is a casting bar, that appears on top of his title bar that says Twister is casting. At this moment, you just need to start walking. Never cross paths with another player, hence why everyone spreads out at the start of this phase. When the casting is finished, if you see a tiny green twister thing on the floor next to you, do not step on it or touch it."
Slightly longer paragraph, but it only takes about 2 to 3 min. to type out.
I wish people explained it to me like how I just explained the fight, when I was still trying for it. Instead, I got about 15 to 20 deaths from random groups that just simply cannot be bothered to type a sentence.
Then I died another 8 to 10 times with my FC, same exactly problems, the core members wants to carry people through the event, but does a **** poor job at explaining the mechanics and simply just tells people to go watch a video and expects them to clear.