Turn rate -- how to force AI to make gradual sweeping turns, rather than pivoting in place?

I'm working on a behavior which has fireflies swarm around the player once the player gets near. I extended the "wander" node to stop wandering after a random number of seconds and return success, so it can then seek out the player again. Currently, when the firefly changes target destinations, it immediately stops going the direction it was going in and then goes in the new direction. I would like it to be a more like an arcing flight path. I reduced the angular rotation rate, but it just causes the local rotation to be lower. I would like the firefly to always be facing exactly in the direction it is moving (fireflies can't fly sideways or backwards) and always travel 'forward' and when the destination changes, have the firefly gradually change its "facing" angle to face the new destination. This should better approximate forward flight. I'm discussing a firefly, but this is more of a general issue with flying AI.

Here's a video, to demonstrate it:
 
If you are using the NavMeshAgent to move your agent then it's doing the locomotion. There is an angular speed property on that component.
 
I'm seeing the BehaviorTree nodes expose Speed and Angular Speed in the Behavior Tree inspector and override the NavMeshAgent at run-time.

That said, if I change the BehaviorTree nodes' Angular Speed, e.g. to 10, it causes the firefly to "pivot"/"rotate" very slowly, but its actual direction turns immediately. If it's going due north and facing due north, then it has its destination set to due south, it will immediately start going due south and be facing backward as it slowly rotates to face the direction of movement.

How does one make it always go in the direction its facing and if it needs to change direction, do so by gradually changing the direction it's facing. Or alternatively, it can just always face the direction of movement exactly, provided that direction of movement is only changed gradually and not instantly.

Thank you
 
Behavior Designer doesn't do the actual movement and it relies on the NavMeshAgent for locomotion. I have not encountered that before so I would post it on the Unity forum to see if anybody else has experienced it before.
 
Unity Learn has some good tutorials. This is a video from their AI lesson dealing with waypoints but it answers your question.
 
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