While having a TTK and a actual dps number are very similar, they do have slightly different applications.
Especially in the context of “one skill” vs. “the entire rotation”
If you don’t have any way to practiacally/accurately measure the dps of a specific skill it will lead to builds as a whole getting compared, which has upsides and downsides.
Especially for builds that use a lot of buffs and debuff this is way more interesting compared to a pure dps number. Especially when you don’t have 100% uptime on everything.
Here it becomes very interesting, when there would be 3 or 4 different dummies with different amount of HP.
Let’s say one has 5 million, the next one 20 million, the next one 50 million and the biggest one has 100 million.
The same builds would have different “dps” on each of these.
Some builds might be very bursty and perform well on the smaller dummies and other builds might perform very bad on the low ones, but have great dps after a few seconds (builds with a lot of debuff and DoT’s and other ramping mechanics)
For cases like this just having a dps number as measurement is something I actually dislike.
I very much prefer the dummy TTK approach.