Relationship between animator component and timeline animation track

I'm new on Unity Timeline. When I link a GameObject to a Timeline Animation Track, it requires to create an animator component on this GameObject.
I'm wondering why animator component affects Timeline. As I know, Timeline and Animator use different methods to update. What property of the animator component will be replaced by Timeline, only animation clip or the whole component?

 

That's fair. But can we achieve blending two animation tracks in this same timeline? In state machine we can easily access other layers to introduce blending. In my project I want to use additive animation to tweak some details in base animation. I could easily do that with PlayablesAPI. Here is a code example:

Code (CSharp):

1.         g = PlayableGraph.Create("anim");
2.        
3.         var mixMain = AnimationPlayableUtilities.PlayLayerMixer(GetComponent<Animator>(), 1, out g);
4.         mixMain.SetLayerAdditive(0, true);
5.        
6.         var a1 = AnimationClipPlayable.Create(g, _move);
7.         mixMain.AddInput(a1, 0, 1);
8.        
9.         var a2 = AnimationClipPlayable.Create(g, _rotate);
10.         mixMain.AddInput(a2, 0, 1);
11.  
12.         g.Play();

But when it comes to timeline I don't know how can I produce this same result. I am trying to extend AnimationTrack, but it seems like many methods there are not overridable. I've also tried to look at ILayerable from 2019.3.11b, but I failed there as well. Any tips?

 

Any news on this?