i first started doing 8boss on pld with sakpata's/aegis - i do switch to Duban when getting D topfloor objective just oos of the way my group does it, I end up pulling and holding a bunch of fomors while everyone else SCs (this is also the only point where I'll use my SIR set). Once I got Burtgang it's just Burt/Aegis.
Obviously Excal/Aegis for Aminon.
HolyCircle and Sepulcher as stated on C/G - Holy Circle also works to give everyone an extra buff in case Leshonn is in WindHands so there's more buffs to potentially get stolen. Also recommend Accession Firestorm and Aquaveil for those extra buffs too, and firestorm may help COR dps on A/E/C/G if they are using HotShot.
I don't worry about contributing DPS really but I do engage and WS on all bosses we don't kite.
I use Fealty before going in if Leshonn is ThunderHands so I don't get stunned a bunch at the beginning, and you can also do the same with Tribolouex since he will stun at the beginning sometimes.
For Gartell specifically I just always stay 20+ away even on the initial pull so that he doesn't ever have a chance to do any TP moves since getting one of our songs stolen there means we're down a buff until CC comes back up. Not a huge deal but this can really make a difference if you're trying to squeeze in 9boss