I have a lv90 WAR myself that isn't far off BiS including the Savage pieces. I never run duty finder dungeons on it. I leveled with Squadron and Trust in the past and in this expansion it was my class for farming FATEs to unlock the 60 shared fate bonus in each zone. I keep it primarily for Hunts and just to have one, but occasionally I'll tank raids for FC for fun.
Basically I'm just saying having a level 90 tank means nothing about your dungeon experience. Not everyone is a roulette addict. Also you have to start somewhere, you shouldn't be locked out from learning just because you reached 90 through other means.
In your case, your tank had a great attitude and whoever the player in dark red is, they quite frankly had a terrible attitude. Players like that are the reason we have less tanks in dungeon queues.