Tanking

This is an equation though.

If I ask 'why can't a Fighter/Tank be a tank', here's what prevents that overall.

1. Can they do more DPS than a tank?
Probably, or we may not see a lot of Fighters...
2. Can they find a way to take near or less damage than a tank?
Probably harder, but most of the tank abilities so far don't do damage reduction consistently, or other classes can help provide a lot of this.
3. Can they control adds (for some this might even be optional)?
Dunno, but this is pretty binary.
4. Can they match a Tank/X's bonus to Threat?
Not saying I know, here, but if the answer is yes via augments, then the equation's done.

This class has all the abilities of a Fighter, and outperforms the Tank at Tanking in at least some groups, where 'Ultimate Defense' isn't necessary for whatever reason.

Are we assuming that Bulwark and Ultimate Defense are such powerful damage mitigation tools that nothing can match them?

What I mean is this (I'm often the tank or the healer or sometimes both for my group in nearly any MMO).

Let's assume that I have one DPS player who is doing 200 damage every 30 seconds.
My tank character does 100 damage every 30 seconds, generates the equivalent threat of 200 damage through abilities, and takes only 75 damage, in that 30 seconds.

I hold the enemy.

If that DPS player does a big ability and takes attention for 10 seconds, and then take 50 damage, multiple things happen (you're a tank so you're obviously familiar with all of this but humor me).

1. I didn't take that 50 damage so I now have 50 additional 'hate'.
2. They lost 50 'hate'.
3. The healer got a little more (but probably not because they'll use Regen instead of a heal)
4. The enemy returns to me. This is a given. The gap between my DPS and their DPS is 100. They lost 50 'hate' and I got to 'keep' an extra 50.

There's only a certain amount of time before that disparity returns the enemy to me, because if it does not come back to me, then it means I wasn't generating much more than they were to begin with, and therefore I was failing at tanking.

So, right after that big burst, which we can say brought them to 'some amount of hate higher than mine', I 'lose control of the enemy'. But this is a whole strategy that is employed quite often. Let the DPS go a little wild, you get more damage and the healer often uses LESS mana relative to the fight length.

DPS characters have to be so squishy for this to be a bad idea, that it's a little weird to be concerned about it (because if they are, PvP will suck).

Point of all this is, Tank doesn't currently have any abilities other than Ultimate Defense that will definitely cause the damage mitigation to be so much higher than damage mitigation available to other classes, to go 'this is definitely the only tank for all content'.

What they have is all of the 'I can stand even when things are going bad and I have no support' damage mitigation. Other tanks are often better, when supported, than the 'standard tank class'. All you have to do is change the 'random DPS' in the above scenario to 'X/Tank'.

In most games, almost the only thing determining 'if a class is actually a Tank' is if they can manage DPS on the target and not take more resources than a 'standard tank' to keep alive. And what stops most from getting that designation is that the enemy, in some way, prevents them from doing the DPS, and the 'true tank' shines because they just use an ability to generate threat instead, that can't miss, or something.

I think that the main thing here might be a philosophy thing, (from Intrepid's side/Steven's mind, rather than between the posters discussing things here).

I can tank in many groups as the healer because of community. My group knows what to do, they know how to rotate things, they know what to expect and when to hold off on their abilities because of my rotations.

In short, the social aspect of the game has opened new opportunities. Sometimes opportunities that other groups don't even have because 'this fight requires more healing than usual so the healer is in danger' so the tank choices are limited or need really incredible gear or skill.

I can't say if Tank will get a true taunt, or if they'll be expecting people to rely on Weapon Throw. And we don't know right now, if the ability can miss in a way that cause zero threat generation, do we?

I guess in the end, we're both (tentatively) reassuring people that X/Tank works in way more situations with even minor tweaks, and we've probably said enough. Those who are still really worried after this point, I really hope you don't get too discouraged.

Know that even if you don't have the time to give a ton of feedback on it yourself if it somehow doesn't get designed right, you've got some Alpha Tester 'tank mains' on your side.