A lot of resource generation is tied to taking damage, or mitigating damage, so dummy runs are awful. Even off tanking won't give good numbers. Nefra is probably the best example to compare you with your co-tank since you take equal hits.
Gear will have an effect too. Endurance heavy 'B' mods also come with lower main stat and a full set of def/abs augments add a lot of power. So make sure you're comparing apples to apples first.
Other more credible folks have claimed guardians all else being equal will be 100-200 or so dps lower than shadow/vanguard.
Very much this. Even more so for guardians since Riposte is such a very important skill for both threat and DPS since it can't miss. But on a dummy you can only use it after guardian slash. When you're tanking you can use it on cooldown a lot of the time. On something like Tu'chuk, when you pop saber ward, the cooldown goes to 1.5s and you can use it everytime it's up which will shoot your DPS and Threat through the roof (relatively speaking). All of that also made possible with the aforementioned much better focus generation when you're actually taking damage.
Parse on some bosses and see what the actual DPS is. Keep in mind times you're tanking the boss vs when you aren't when comparing to other tanks. For example, on Writhing Horror or TFB, you'll do a lot less damage, and generate a lot less threat, when you aren't a main threat target for all the reasons your dummy parses will suck out loud.
Now I'm not saying suddenly you'll shoot to 1600 DPS on a boss clearly, and KBN's point about his gear is very well taken (plus in general KBN is a pretty good player and is maximizing his threat, part of which includes having as high damage as he can within the constraints of being a tank). That being said, much more than any DPS, a dummy parse is super misleading for any tank.