I do agree that blind not really effective on a lot Endgame boss, so far Garuda EX when tanking Her and sister is always a good idea to blind b4 they WW or down burst. ( i dodge a few what way.)
on Single target. You do not flash for Emity, you flash for blind. (unless you want initial snap aggro form newly spawn add otherwise you spam RoH combo).
Flash for Emity only a good idea when AoE tanking and snap aggro on newly spawn add.