The simple answer is NOT to remove any one class, but to make the content challenging enough and remove the ability of dps to take more than one or two shots from a (group) boss much like it was in prior content. Taking the defense rating out of the game was a very silly mistake on blizzard's part. There was a mechanic that in one fell swoop added the ability to keep dps in their place. As tools to bring a target's health down. Mine is to fix it in place while you do so.
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This being said it would point to there NOT being a shortage of tanks. Maybe there is a shortage of competent players who are filling the tank rolls, but LFD is not built around the concept of any competency being needed.