DPS meters and gear scoring have caused more problems than they've ever solved. FFXIV shouldn't have either, period. I hope you told him to shove it, and reported him.

That being said, Garuda isn't a good way to gauge a caster class due to the insane movement, and we have no choice but to interrupt spells. Even spamming Swiftcast every time it's up, or every instaproc, melee will win in the DPS race there. Others will probably have some valid suggestions for you on an optimal rotation, I'll stick to healing until some of the freeloaders leave and go back to wherever they can inflate their e-peens a bit more.