EDIT (March 9th 2021):
Solved in 6.9 and up. Reformatting the cache to new partition alignment and hosting docker directly on a cache-only directory brought writes down to a bare minimum.
First of all, I know that you're all very busy on getting version 6.8 out there, something I'm very much waiting on as well. I'm seeing great progress, so thanks so much for that! Furthermore I won't be expecting this to be on top of the priority list, but