nice try you only focused on one thing an not all of what i saidan fyi i didnt bring up new players you did. everyone knows when someone is new it literally pops up in their vision at the start of the dungeon or raid or trial an if the new player asked if they could do a re-try most times the tank will be nice an say yes an no big deal for them.
and with tanks yes keeping enemity i/e distracting the enemy is part of their role but see you focused in on only one thing or word i said an are not crediting for the rest when their is no healer alive then it falls to the tank to use his/her mitigation to maintain the enemies focus for as long as possible until the healer can get back up or until they kick the bucket too just as its the DPS' job to kill everything dead an make sure that it stays down so that the fight can progress or the dungeon can progress people make mistakes do you see the party getting mad alot when the healer drops dead an insult them or get mad about it? no you dont an usually people who are jerks about it get kicked or pay the GM a visit in Gaol lol so let me ask you should you not then extend that same courtesy to the tank when they are trying to just stay alive long enough to see the duty to its completion?
like i get it you're mad you didn't get to play cause of one mistake or misstep but again that would be your own fault and it would be a flaw or problem with the encounter itself its not the tank's fault they are doing what they were designed to do Survive long enough to reach a duty completion screen while having held the enemies' attention the whole way thru.
so be humble try playing a tank for one whole week i promise you will change your thinking right away an will be thankful the healer was at least "just there" to assist an make things a little easier an smoother even if they nose dived at the end you are not mad at them just glad they stuck it out long enough to reach the end period.