It's not that locks were FOTM in Mists (although I agree the damage output made them FOTM to some). It was more that the massive revamp actually made all three specs unique and fun to play. Blizzard then chipped away at the fun nerf-by-nerf, patch-by-patch, xpac-by-xpac, so that locks specs are no longer fun nor unique.
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Agreed demo has always been a favorite, but after leveling as Demo in Legion I couldn't stand to hit DE anymore. I can't wait to go back to demo in BfA
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That's why I am hoping implosion is baseline in BfA. Having the snap AOE in your back pocket without having to waste a talent slot would be fantastic.
You forgot about life tap!!