Ok there should be a easier way to get bark or you should be able to use plant matter as a alternative fuel source.
The process isn’t about burning the hides. I may be wrong, but tanning leather uses acid to treat the hides. Best source for the right acid is, you guessed it, bark.
That said, use the pick on trees instead of the axe. Bark is much more useful than branches. Turning branches into bark on the carpenter bench would be nice.
Or as was said on discord, and other topic right here (I guess) making bark sideproduct of making shaped wood in carpenter’s bench.
There is a better way. Don’t get it from trees, get it from NPC settlements.
I typically get multiple stacks just from clearing the main camps, such as The Den and New Asagarth. The artisans and chests have a lot of it. Fighting for it is faster, far more profitable and a lot less boring than picking at trees for hours.
And don’t waste your steelfire on making steel… You can get tons of steel from New Asagarth. Now you need a lot less bark