Suramar Dungeons have been locked behind quests since the get go. The only reason they were available without Suramar was for testing purposes but now that Suramar is actually working and they don't need to focus on dungeon testing, they put the requirement back on. You say you were looking forward to an endgame zone lasting longer than 3 hours and yet you're complaining about content being gated... what?
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Oh wow yeah totally, Flying unlocked the Dark Portal (uninstaned Tanaan start experience), uninstanced HFC 1st and 2nd boss room and uninstanced Highmaul. So much content.