Do you think that if a player completes LFR and/or even Normal, then they have completed 100% of the raid content in an expansion?
Personally I don't think so. If you put the amount of raid content on a straight line and the line is raid content, and it is divided up by the difficulty levels, then id say a person who only completed LFR would have only completed maybe 5% of the raid content of an expansion.
Just as an example:
LFR = 5% completion
Normal = 20% completion
Heroic = 35% completion
Mythic = 40% completion
If a player were to complete all of these difficulties, killing every boss, then they would be at 100% completion of the raid content in an expansion.
Do you agree / disagree?
So if a player only completes LFR and does heroic dungeons, have they really even nipped the surface of the expansion's content?