I found nice a 7th rock to do which could replace the very 1st rock which was the 1st experiment.

About experiment, just a reminder : what I do remains experimental ; I remain -& define myself as- an amateur so what I do is not perfect nor as optimized as it could be in a professional way.

That said, Duion pointed that my way was not optimized for ingame usage (1 UV+texture per LOD is not ideal). They only fix I found about that is combining them all into a single map & doing the UV layout in consequence like in the "LOD_Atlas.png" attachment.
I tested it, it does the trick. I also can ditch the 64k LOD and add 250 + 125 tris LODs. I can even have fewer LODs.

Then Vital de la Torre talked about a software -Atangeo Updater- which does the kind of the stuff meshlab does well too except the decimation with texture which doesn't work for some reason. =|
It's not visualy as perfect as I did so far but I think I'll use it for the future assets.

This asset is licensed under CC-0 (4.0 or later) 

-Yughues

EDIT: erratum, Meshlab decimation with texture works, someone found a workaround to fix the issue... So I spent money ($52) for nothing. Logic & reason vanish when I'm upset.

 EDIT2 : added a 4k² textures version (1k² for occlusions) + better files   naming for consistency with newer rocks. Multi-archives due to Patreon   file size limitation.