If the combo doesn't work stop using it. You can land Phoenix or Fire Grab even without any CC and they both hit harder than DT, you don't need your target to stand still for anything but DT. You can also use Earthquake -> Phoenix, or Earthquake -> Drake's Breath for 1 tick -> Fire Grab both of which can apply Grounded bonus if you choose to take it. Gale on the focus can substitute Earthquake. Updraft -> Phoenix is close but I'm pretty sure you can land 2/3 of the hits before they can move. The desire to land the "full combo" is just going to make you waste spells that you could land if you cast them normally. If you want to land Dragon's Tooth use Signet of Earth or Deep Freeze on the frost bow, either lasts long enough for DT, Phoenix and Fire Grab all together.
An ele's combo (with DT) takes 4 or so seconds to fully execute, with a 1 second (or so it seems) window for the enemy to stunbreaker or otherwise move out of the DT red circle, meaning his whole combo is suddenly for naught. On the other hand, thief can execute his combo in under 1 second, invisible the entire time, and hey, if that doesn't work, hit a HS or two to finish them off. In short:
Ele's have to hit a still target, while thieves can do as much damage, if not more, while invisible, instantly, on moving targets. As if that's not enough, a Ele, when his combo is over, cannot simply just shadowstep away if the target isn't dead/enemy countered his combo. A thief can do all of that and more.
I don't know what you guys expect when comparing ele to thief. Ele has AoE burst, and they can still land single spells for 6-10k and add instant damage effects on top. If you don't like a glass cannon ele fine, don't run it, I prefer air/water/arcane Valkyrie's builds myself, but don't claim our damage is bad because you wont run a build with as much power and as many +% damage traits as the thief you are comparing it to. Even if you run a berserker's amulet you can still expect a 30 water 30 arcane build do do a lot less damage than 30 fire 30 air, and that's what you should expect. I never said thief burst was bad, or even balanced, I said ele damage is comparable if you actually compare builds with the same amount of damage traits.