There is literally no comparison. My Guild has been consistently completing Heroic Rancor in approximately 14 minutes since the introduction of Vader's Zeta, but we only just managed to complete the Heroic AAT for the first time a little under 2 months ago, and it took 95% of our Guild participating in unison. With our recent strategic and character improvements we can now complete it in approximately 8 hours with good RNG, but it's still no cakewalk, and that's coming from someone whose Guild has 9 people regularly solo the Heroic Rancor, including myself.
My advice: play Normal AAT, upgrade your characters throughout your Guild, ensure that you have at least 40 dedicated players who can communicate and commit to a scheme for taking it down, and make trial runs on Heroic AAT every now and again to assess your strength. You'll make it eventually. Best of luck to you!