I was really trying to avoid this, using everything stock, and debugging, but at some point need to give in to the “hacky” approach, bit sad 
For those looking for a similar solution. Add this to your init/shutdown scripts:
echo 68720000000 >> /sys/module/zfs/parameters/zfs_arc_max
Add it at post-init
Adjust the number 68720000000 to the ram amount you want to assign. 68720000000 is in bytes, and in my case equals 64 GiB. Use wolfram alpha for your own calculations 