Blizzard have announced that they will be buffing mob HP with the upcoming Beta build and explained the intended average combat duration.
HP Increase (Source)
When we next restart the Dragonflight Beta realms, we will increase enemy health to bring combat times closer to our intended targets.
Our expectation is that the average player going through a questing experience with one of the standard template characters will be engaged with a single enemy for one or two durations of their typical damage rotation. There are many players out there and they all have varying skill levels, and we expect that different players will have different experiences with these changes.
Please let us know your thoughts about this here, in this thread.