Astrid,
I'm having trouble following you, but I do think that you need to make sure you understand what you are looking at and what you call things.
The Fitted Mesh Survival Kit, which you propose is wrong, is not Avastar, and it's only real association is that we supplied it. It is merely provided to give users, who do not have Avastar, a way to use the mesh and rig, provided by Linden Labs, for Fitted within Blender.
As Gaia stated on the Fitted Mesh Survival Kit page:
"All previous versions of blender can not create Collada Files that work with fitted Mesh, because Blender does not support a customizable restpose matrix (or bind pose matrix) as it is available in Maya. We have added a workaround which allows to export the data so that the SL Importer is happy again."
Statements you made, such as "Below you can see the proof that avastar free avatar and second life free avatar are the same thing, with same “bugginess”: I have applied the same scale values to BELLY and PELVIS bone and you can see that butt gets oddly distorced." would thus be incorrect. It isn't "proof" when we've already stated that it's based on LL's work.
What you are calling "avastar free avatar" is a misnomer. I am guessing you are calling it that because we mention that the file is provided for those without Avastar; that doesn't make it "avastar free" or free of avastar. The more accurate reference would be, "The fitted mesh survival kit".
You are making quite a few assumptions. We always welcome comments and questions. We only ask that you be clear and, rather than assume, ask us and we'd be happy to explain.
Thank you,
Eleanora