There is a reason for what you see on the screen, but you can only know whats going on if you played the game, Bosses in BnS had similar mechanics as bosses in other games like wow or Ff14, but was more focused on action combat, for example, there are no tanks, healers or DPS classes, everyone is DPS essentially.
You can turn off the camera shaking but this player decided to keep it on, you can toggle off other players the same way to toggle off spell effects in FF14, for visual clarity or performance reason.
Bosses in BnS are mostly dodging, blocking or iframing attacks, he only got hit twice in the entire fight, and one hit can be enough to get killed or wipe if the tank gets knocked too far away from the boss, there is a lot of boss positioning going on so the boss doesnt hit the rest of the party, you had to stack players that get aired and juggle a fireball, you had to block rockets at the end by activly using your "block" skill and not just stand infront of them.
They killed the Boss 1 second before the enrage, when the raid content was brand new, thats like clearing Savage in week one.
Why Blade and Soul failed has vastly other reasons than the combat, which was probably also too difficult for the average player.
Yes, obviously FF14 could never work like BnS combat, althoughsome jobs do have dash abilities like dancer, but they play no important role anywhere, you can do any mechanic without sprint or movement skills.
BnS is not button spamming, you can hold down the right mouse button for your auto attacks but the global CD is almost non existent so you can use a lot of skills at the same time, that really only depends on your Ping.
I played BnS a lot before i switched to FF14, the difference in pace was shocking at first, everything felt so incredibly slow, but the onyl thing i want them to change is the damn "auto turning to the enemy", that is absolute dogshit to play against.