after leveling Paladin ... Dark Knight just feels really squishy

[Gemina]

Popping your defensives during a pull is actually very inefficient and tends to result in wasting most of the up-time on them. With all defensive cooldowns that are gated by a recast timer you want to maximize their effectiveness by timing them with the greatest periods of incoming damage. In a mass or long pull that tends to be approximately 2 or so seconds after you stop when all the enemies, including the stragglers, have caught up to you and are now attacking you.

I personally tend to queue up Salted Earth so that it is ready to be placed as I am getting near to stopping, place it where I will be tanking, spend approx. 1 or so seconds making sure positioning is good. At this point the enemies that were chasing me should be catching up so I pop whatever defensive I will be using for this pull plus Blood Price, throw out my initial burst AoE enmity to build my cushion and then start in on my AoE rotation.

I totally understand where you are coming from when it comes to uptime. Proper/optimal CD rotation is going to be efficient by pure happenstance. Using a CD during a pull is more aimed at Anticipation than Awareness. Being on a 60 second cooldown means that you are going to get more use out of it the sooner you use it. Depending on the groups DPS, you'll be able to use it multiple times during a large pull which entails the pull itself and the stopping point. Your stronger mitigative CDs should definitely be held until the stopping point to maximize how much incoming damage they shave off throughout their duration because every single hit is mitigated while they are active. For something like Anticipation, which only increases the rate at which you parry, you can be much more liberal with its use. This can also apply to Awareness because mob crits are also RNG dependent, but the two minute CD my advice and preference is to use it depending on the situation.

In terms of Salted Earth, the uptime is also a factor and because of this I prefer to weave it between GCDs. You want to maximize its damage along with how much it fills the blood gauge. Pre-casting before the pull is done is going to easily lose you 1-2 ticks, and the amount of damage you lose increases the more mobs you pull. We have to remember that bubbles now immediately activate upon their use making weaving them much more optimal.

Really one of the best "defensive" abilities to use during the actual process of pulling is Sprint. If you put enough distance between yourself and the mobs chasing you by outpacing them slightly, they can't hit you and you take little to no damage from them. Just keep in mind where the rest of your party is and ask them to use sprint as well if they keep falling too far behind.

While I do agree here somewhat, sprint isn't required to outpace mobs. There is no avoiding damage entirely during the pull no matter what you do because you're going to get auto attacked once you're in range, very similar to why you will always see your own auto attack in the log before your weaponskill in your opener. Also, using sprint in a PUG often has lead me to taking even more damage because healers tend to not even know it exists outside of sanctuaries. If you know you have a good group who is going to keep up, sprint can definitely be used to help create distance between you and the chasing mobs.

While you may mitigate a little bit of fluff damage by popping your weaker defensives during a pull, as you said, you should be using those weaker ones in your basic defensive rotation. As has been stressed before, while using these weaker defensives by themselves may provide little defense, stacking them together can pretty much make them just as effective as something like Rampart.
Anticipation is on a 60s cooldown and so can be used almost , if not every large pull. It's availability makes it good for popping after your main defensive has run out and you want a little more protection until the mobs have been thinned enough to where their damage is negligible.

I would not underestimate how much damage you take during a large pull. Yes, you want to rotate your CDs so you always have something to use when incoming damage is heavy, and use a strong CD in combination with a weaker one. Your strong CDs are Shadow Wall and Rampart, and the weaker ones I use are Convalescence and Awareness; throughout my days of pulling as DRK, Anticipation has been able to be used far more liberally than anything else because its CD is so short. Basically, pop it whenever it is up and you're also getting hit. Also have faith in your healer until they show otherwise, and don't forget you also have Living Dead.

Honestly, the biggest problem with DRKs mass pulling while not having TBN is that they don't have the necessary synergy of TBN and Quietus to fuel their basic AoE resource gain which is kind of necessary for taking on large groups.

Not true. I've been mass pulling with my DRK since lv50. After level 50, we don't get a single mitigative tool until lv70. You have to make use of your other abilities such as DA+Abysmal Drain, Sole Survivor and Blood abilities to either increase timers, replenish MP for more ADs, and kill things faster. Mass pulling as DRK is seriously a lot of fun even before TBN. Again, if you learn how to sustain yourself prior to getting it; it only makes it that much better because it essentially becomes a very fast way to fill the Blood gauge at that point while also reducing damage.

Overall the best thing any tank playing any of the jobs in any dungeon content can do to increase their survivability is to pay attention to and learn the dungeons so that they learn the pulls and what defensive cooldowns they can pair with them.
Learn and plan ahead and you should do fine, only play reactively and you're going to have a bad time.

Totally agree with you here.