You're building the entire basis of your argument on a faulty foundation. Sim dps has exactly ZERO to do with the discussion at hand. Your statement completely disregards the bell curve in SimC's results. That 720k doesn't mean that it's the max possible DPS for your gear. It's means that 720k is the AVERAGE dps for your gear, when played optimally. Roughly HALF of the sim results for your gear fall ABOVE 720k. Higher than expected crit rates, nice proc strings, etc all account for more than the "expected" 720k....and guess what? Real life players actually experience those situations in game and their parses go into warcraftlogs. Your parses are measured against those when determining percentile.
To say "boo hoo I don't have BIS legs ergo I'm gimped" is to lean on an imaginary crutch. Good players should be parsing 90-95% even with garbage legendaries.