Yeah tanks' DPS rotations are quite basic compared to pure DPS jobs, but DPSing as a tank isn't limited to get STR and do 1-2-3-1-4-5-1-4-6-repeat. It highly depends on the encounter, the incoming damage, and how you plan on mitigating it. You cannot go nuts on DPS 100% of the time as a tank, and knowing when you can do it and when you have to mitigate is what makes the complexity of it. There is unfortunately plenty of bad tanks who solely focus on DPS and get destroyed (then generally complains about healing). These are people trying to DPS, but failing because they don't know how to mitigate while doing it. These people certainly know the DPS rotation of their tank job, but they don't know anything about aggressive-tanking. Proper mitigation is the key to achieve high tank DPS.