Well said Rosy. Here's a conversation I had with a friend of mine (playing on another server) that's quitting, and why:
They're on a hardcore server where everyone expects you to immediately read up / watch YouTube videos for the latest patch contents to prep or you get kicked.
"I just got tired of having to 'research' every new fight before I could experience them. When you think about it, it's totally backwards: Since you essentially have to memorize each fight on Youtube before you try them, everything is spoiled. There's nothing new or different to discover. You've seen every move and attack a dozen times on video before you've even begun. My first fight with Leviathan was totally boring rather than exciting. It's all rote memorization and twitch reactions (and hoping lag doesn't kill you regardless). That's fun???"
And when you can do it flawlessly, unless you have a static, you have to find 7 other people to do the same perfect "dance" / routine with you, or else you lose, even if you didn't make any mistakes.
That's one of the biggest flaws. It's fine to have challenging content, but the way they've designed the fights to be, one newbie messing up on DiveBombs can cause Twintania to knock the Tanks and/or Healers into the Flame Walls, one-shotting them along with the newbie.
Other MMOs have fights and raids where a mistake and wiping ended up with an *understanding* attitude and sometimes some good laughs and you retry. In XIV, the way these end game fights have become it's like what the OP says: It's toxic and everyone gets mad or frustrated and quickly Vote Disbands / Rage Quits. There's no feeling of exploring the fights and being challenged by them either, after you memorize it (I've memorized all the EX Primal fights and have cleared them repeatedly). It really is just memorization, and hoping you have 7 other players that memorized the routine with you.
It should be more interesting and engaging than this for Hardcore and Mainstream, while also having more room for error / recovery for Mainstream players (so if they screw up Landslide, DiveBomb, Twister, Acid Cloud, etc., etc.) it's not instant death or an irrecoverable wipe. Some posters brought up good ideas in this thread, like perhaps Landslide will knock you "off" but you can still climb back up (however they sell that), or the rage timer is more lenient to allow mainstream players to recover from a few deaths and still eventually beat the boss if they get that far.
I sincerely hope the Dev Team considers these things going forward.