Thanks to Danelin, very interesting post. Also the way you categorized and explained your view of the fighter subtypes is a very good approximation to how I see them based on the same years of rpg/mmo play. So good on you man, it is nice to agree with someone for a change 
. Would be good to have somewhere in the replies approximate the numbers as they should be for the rating to balance things out.
The problems I see are in the implementation of the paradigm as you describe it. Basically, the paradigm initiates several questions in my mind.
Via this paradigm then the tanks might be relegated to the following?
a) guardians and paladins would be your best raid MTs/STs.
b) Berserkers and Shadowknights would be your best group tanks.
c) Monks and Bruisers would be hands down the best soloers.
That seems like the practical side of how it would be implemented. So the big question becomes, how do you even out the abilities of the fighters so that the different groups a,b, and c above can find roles outside of their group? Or do you even try to do that?
It seems like you could try to allow 2 of the 3 roles I am mentioning with stances or abilites. For example, a guardian could be a good group tank by upping his offense in some manner. Also, a monk could tank for a group by upping his ability to mitigate. Finally, a berserker would be able to MT a raid by having a way to increase his toughness. However, I don't think it would be possible for all tanks to fill all three roles. Seems like trying to do that would be almost impossible without a ton of imbalances.
Then there is, of course, group and raid usefulness. It would be nice if it were possible for there to be more than 4 tanks in a raid and for it to be a valid configuration.