LFR is still the more popular mode, by far, though. by faaaaaaaaaaaaaar. Entirely different audiences, really, too. The people whom really need LFR are probably never going to touch Flex or anything higher, and that tends to be the majority of people touching this content at all, so, naturally, those people should be catered to. I don't see a logical reason why they shouldn't.
However, they probably should find a way to bring the group-size mechanic of flex, somehow or another, into LFR, too. Or something to that effect. Maybe. I don't know! but LFR isn't going anywhere. It's just too popular, and serves too great of a purpose.
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Very few people actually doing it watered down and diminished the quality of raiding :x
Clearly, LFR was made for a reason, yo.
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I imagine the amount of people who drop out of normal or above raiding is minuscule compared to the assumed gigantic amount of people whom had never raided before, whom now benefit from LFR.
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A large portion of people can't even grasp that concept, and think everyone who plays WoW wants to be doing things with large groups of friends/a guild, despite historical evidence to the contrary, and being unable to see past their own experiences, and see the actual reality of the situation. (i.e. these things were all done for a reason.)
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It's not about wanting to learn to play, I truly believe, as it is about not wanting to do organized activities with a large group of people who will inherently judge your every ability and action. The very concept, to a lot of people, is stressful, and not something they want out of a videogame.
Now, there is an argument to be made that these people should never of been playing WoW in the first place, for true. But that's the majority of the people playing WoW now, so Blizzard has to deal with the hand their dealt.