I hear ya Anzak, here is my slant on your questions:
(1&2) I really dont subscribe to the guardians and berzerkers being one trick ponies, it is more of creatures of habit being use to only the main tank then anything else. True the guardians do have some combat arts that should be tweaked, but most of those are similar to pallie spells that should be tweaked. If SOE would only fix the intercept line for fighters, they would have tremendous potential for offtanking and protection of other classes(like protecting that wizard with intercept but use the guardians mit for the check) As it is right now versus tier 7 mobs the inherent skills like the mit buffs for 30 seconds/tower of stone and a few others make it easier as a raid to have a guardian or berzerker(minus tiwer of stone) tank in like gear. All we can do for now is keep posting for positive changes for us and hope that there is a logical plan for us in raiding as mt in the future.
(3) is that mit aa a ability from the swashbuckler class or another? If from the swashbuckler i could see that as benefical, especially when soloing. Any more i try to ask for any changes in other classes but try to ask for positive changes in our class, it just opens up too much flames from the accused class. I know you are not asking for a nerf Anzak just stating my opinion on it, heheh.
(4) about the only situational tanking i have seen for us has been the black queen before KOS, where having a large magic resist was more important than a extra 300 mitigation. I still hope they will change/revamp or add content that is all or almost all damage from different spell types: heat/cold/mental/magic/disease/poison/divine with little or no melee damage. There have been enough posts that SOE can not claim they have not ssen this request...

(5) I agree also on the resists, by now i have deciced that our stamina end AA divine aura is too nerfed to matter much for the 8 points you spend for it, i almost wish they would just revamp the spell and give us a passive ability that gave you a 2,000 to 4,000 boost on all your resists instead. We are labeled as caster/resist tanks and that change would allow us to keep higher mit armor and retain high resists too.
(6) The avoidance tanks are not faring well against tier 7 mobs at all from what i can see. Not factoring in the lovely mitigation debuff abilities that seem to be on every other mob in KOS, the epics are hitting way too much and hard for a raid equipped avoidance tank to take. In group sitations, the avoidance tanks are doing good, but the raid mobs are just too pwerful anymore.