Here are the principles of bone control over vertex groups:
Let's say that I have a bone called Bone1 and a vertex group called Bone1 as well. The bone will control the vertex group that has its name (if it has been parented with an Armature Deform option). Here I assign a vertex group weight of 1 to the 2 vertices on the left, and a weight of 0.1 to the 2 center vertices:
If the center vertices are only part of this group, it doesn't matter how much is the weight, as long as it is not 0 of course, they will be influenced by the bone as much as if they had a weight of 1, see what happens if I move the bone, left and center vertices are equally moved by the bones:
Now let's create a new bone, called Bone2. I create a second vertex group called Bone2 and assign a vertex group weight of 0.1 to the center vertices, and a weight of 1 to the right vertices:
If I move Bone2, as the center vertices are now part of 2 vertex groups that equally influence them, they will be equally stretched between the 2 bones:
Now, for these center vertices, if I change the weight of Bone2 up to 0.5 instead of 0.1, this time the influence of Bone2 on these vertices will be 5 times higher than Bone1, and so on:
All this explains what you show: You think that the weight of the bone should smoothly decrease along the mesh, but it's not what happens:
Why? Because the vertices that seem only lightly influenced are only part of this bone's vertex group, so the influence of this bone on these vertices is as strong as if it was 1. To decrease the influence of the bone on these vertices, they should be part of the next vertex group as well. That's what you need to keep in mind when you parent the tank track to these bones. Parent With Automatic Weight should work, because it will smoothly share the vertices between the groups, but you can do it manually if you keep all these principles in mind.