Originally Posted by
kneehidude
I'm sorry, but your posts come across as someone who has never raided mythic (old heroic) ever. I'll address the bolded points one by one.
Watching a video doesn't mean you "know the fight" all it knows is you have some basis of an idea on the fight and know things to watch out for. Watching the fight once on youtube does not mean you are going to go in and perform all the mechanics perfectly.
Previous experience, while good doesn't mean you know the content. Yeah, you may have the skill but first time on a boss is still first time on a boss. You're going to make mistakes and it's going to take some time to learn the fight well enough to not make mistakes.
Previous boss kills matter because if I am a pug leader putting a group together and some guy with no achievement and no experience whatsoever says they're good, I am not going to believe them. I have no gauge of their skill, I'd have to take their word for it. At least if they had previous boss kills leading up to the final boss that the group is working on, you could reasonably assume they have experience with the content and have probably seen the fight at least a few times.