Is there a way to disable the tree foilage for leaves? I personally think it doesnt fit for my barebones texturepack :>

Hey, you can go into the packs folder and navigate to this dirrctory:
assets/minecraft/blockstates/
In there just search "leave" and these files. This way the game doesn't know that the leaves even exist.

If there are still problems goto:
assets/minecraft/models/block/
And delete the folder called 'leaves'