For those like me who are trying to do Legion Assaults in 2024 and beyond, please be advised:
1.) When you reach the part of the quest where you are put onto a "vehicle" and are required to shoot balls of arcane energy at the Fel Orb atop the tower, you'll need to make sure that you aim your attacks underneath the Fel Orb, and you need to make sure you are seeing floating damage numbers to ensure you are aiming at the proper spot.
2.) Once you get the aiming down, log out, and continue to spam your "2" ability at the Fel Orb until the 20 second logout timer is complete. Once logged out, immediately log back in. You'll find yourself dismounted from the "vehicle" near the initial quest giver. Walk forward and mount the gryphon again. Repeat step 1.
3.) Rinse and repeat 3-4 times and you'll complete that part of the quest.
Enjoy!