Tank here. Sk tank in the days when Shadowknights caused an xp hit for the whole group. But my rep was such that nobody cared. I had instant group invites when I logged in (miss the days when server rep mattered). That rep also got me into the top guild where I was the prime trash tank, which meant tanking everything except the boss.
All tanking done in first person, always, for years.
I never played in 3rd person (hated 3rd person games anyways) except when I was fd and checking out spawns. First person was very viable in EQ, even for a tank. Personally, I think it gave me an advantage over the slower players using 3rd person, but that was because of EQ's targeting mechanics. It also helped that I came to EQ from fps games and that it took a doctorate to use 3rd person in EQ before they fixed it.
I still prefer first person play, but now every mmo is designed for 3rd person and first person, if it exists at all, is just a gimmick. A mmo that forces players into first person would be cool, not sure how well it will do though. So many mmo players are incapable of playing without their 3rd person crutch.