Enmity can be a bit wacky at times but from what I've observed single mob enmity is not broken, but multiple mob enmity is, however there is a solution for that too.
I've seen Glads successfully hold aggro and I've gotten to a point to where I can hold aggro as a pugilist by DPS as well as my actual tank abilities.
Properly tanking in this game isn't facerolling your sunder key, it's a dance and is a very reactive game. Most tank abilities only work after you successfully evade, parry, block, etc... and if the tank is spamming an action they will likely miss that chance. For example my highest threat ability only works after a successful evade, if I'm not keeping Featherfoot and Light Strike up, my chances of that aren't great. It also adds a stun which is a nice damage mitigation. The way your gear is laid out also has a big effect on a tanks chance to parry/evade/etc...
For pulls where you get more than one mob it's helpful to have a tank on each mob, it's possible to hold aggro on two as a pug but you have to do LOTS of swapping back and forth and forget using your tank abilities. Marauders appear to be your best AoE tanks... The exception to all of this is of course when the mobs keep resetting, which I had happen repeatedly to me last night despite being the MT and group leader, with everyone bunched up on me. Mob resetting is what's causing your enmity reset.
What I've seemed to notice is that each tank type has their role...
-GLA are excellent tanks for really hard single mobs, but fairly rubbish trying to hold aggro on multiple. They also must rely on their shield abilities to properly tank and it may require the group to "slow their roll" so the GLA can establish aggro. Once they do though it is VERY difficult to break that aggro.
-MAR are great for pulls where you get a couple mobs, they seem fairly good solo target.
-PUG are great off-tanks, if played well they can stand toe to toe with a GLA but when you DO get hit you get wrecked.