It seems like the issue you're experiencing with whitespace not being removed during the export of your attachment sequence could be related to how Spine handles whitespace stripping for meshes. When using linked meshes, the whitespace stripping might not work as expected because the mesh vertices remain in the same positions, and only the texture changes. This behavior can result in the images not being trimmed to the shape of the mesh but rather retaining the original PNG shape.

To address this, ensure that your texture packer settings are correctly configured to strip whitespace. You might also want to try using the texture packer separately, as it seems to give you the expected results. Additionally, consider checking if your Spine and runtime versions are up to date, as there might be improvements or bug fixes in newer versions that could resolve this issue.

When an image is used for a mesh, the pixels inside the mesh vertices cannot be whitespace stripped. For example:

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It might seem that the bottom of this image could be stripped, since many rows of pixels are all whitespace from the left to right edges, but whitespace stripping cannot be done there. This is due to technical reasons regarding how textured meshes are rendered versus rending whitespace stripped texture regions. If you use region attachments, then the whitespace stripping can be done.

BTW, I noticed your animation has a number of deform keys. That may be OK, but in general it's better if you can do it with mesh weights. See here:
https://esotericsoftware.com/spine-keys#Deform-keys

Also, it can be difficult to match the movement of multiple meshes when keying their deform. Weights can make that easier, since the vertex movement is based on a bone moving and you can use Weld.