It seems the community of WoW is full of insecure people that spend most of their time trying to insult other people. Reading the forums you can easily see that the number one way to insult people is to say something along the lines of, you suck because you have not beaten raid boss xxx.
This is usually followed by that person saying something in their own defense. This is an alt. I do not play as often as I used to. I am not in a raiding guild. My whole server sucks and no one has it downed yet. You know the line of answers and it is not my place to say if any of them is true but I'll be willing to guess that in most cases they are.
The thing people always seem to forget when they try to insult someone like that is that this is a game, a multi player game at that, and people play it at their own pace and with a different set of people then you do.
You might find Magmaw easy, most might, but for some people it is still a problem. This does not say anything about their personal skill level. It says something about the group they are in.
Raid bosses and their associated raid achievements are not now and will never be a sign of personal ability of the player in question because no matter how good you are raiding in a team sport and your own personal skills, at best, contribute to the success of a raid and are not the sole reason for the success of the raid.
Every person in a raid effects everyone one around them. How they do their job changes how the other around them do theirs.
As a DPS, if everyone else in the group is pulling their weight, you will do more DPS. If you have people slacking and you are trying to push to do more DPS to make up, that is where you will tend to make a mistake and it will actually lower your DPS.
As a DPS, the better you are at managing your threat the better the tank is at holding and positioning the mobs. If DPS does not do their job correctly it makes the tanks job harder and that can cause wipes. Not to mention that even if you have a fantastic tank that can pick a mob off of you the second you get its attention you have now added unneeded stress on the healer because they have to heal you for big damage you should have never received if you did your job right.
As a tank healer it is your job to make sure the tanks stay up, simple enough right? Not exactly. If your raid heals are always falling behind or if they forget to heal themselves, a common healer issue, then you have to divert your attention from the tanks and that could mean a wipe.
As a raid healer you need to keep the raid up. If the tank healer is always falling behind and needs your assistance then you will oom just a bit faster and then people in the raid can start dropping because you are either running on empty or to busy helping on a tank to save someone else.
In each case, the abilities of the healers around you directly effect how well you do your job as a healer. If they are always doing what they should be doing it allows you to never need to worry about anything else but your job which means you can now do your job with more efficiency. This is even more important in the Cataclysm age where you can not throw out the quick big heals to help here and there because they will oom you in no time.
For tanks, they need to know that the other tank knows when to taunt and know that they are going to do it in a timely manner. If they always have to worry about the other tank not taunting when they are supposed to they might end up blowing cooldowns in fear the boss will not be taken and then not have those cooldowns when the time comes that they really need them.
Tanks also need to know that the other tank will not play aggro pinball with them when they are tanking. If the other tank is always accidentally pulling back it messes up a tanking rotation to the point where it could cause a wipe.
Having a tank that can put out massive threat also helps the DPS pour on more DPS. If they are having issues generating threat they are holding back the DPS. Same goes for damage mitigation. If they are taking to many hits they will need more healing which means they are stressing the tank heals.
Tanks knowing when to blow cooldowns help the healers out. If the tanks do not know how and when to use the cooldowns they could waste them when they where not needed.
Raid leading as a whole is a perfect example of that. The more you need to say on vent the worse the raid will go. If you need to call out when someone needs to get out of the group or remind people what to do all the time the chance for error increases. If people always know what they are supposed to do and you do not need to always be telling them. If there are always things being said in vent then the chances of people missing something that was meant for them is higher.
See, it is a complete and total group effort. Any one person doing something wrong means that the fight will end in failure. A DPS that goes overboard and grabs aggro, even for a split second, disrupts the tanks rotation, requires the healer to heal more, might even make the whole raid need to change positions where it could cause a wipe. Needing to help the tank healer means not healing someone in the raid that needs it which means maybe a DPS dies and you can now not make an enrage timer. An offtank pulling back off the tank before it is time and he still has a debuff on him can mean instant death followed by a wipe. Everyone needs to do their job correctly.
Judging a person by their raid achievements is not an accurate assessment of their personal skill level because their personal skills only account for 1/10th or 1/25th of the equation. Anyone on the forums that has to resort to calling someone out saying they suck because they have not down xxx raid is usually the one that most likely sucks because a good raider would understand that one person can not do it alone.
Maybe you can question their choice of people they run with but you can not judge a persons skills as a player based on their raid achievements because you are only as good as who you run with when it comes to raiding.