It’s not always major features like mtl editor. Most projects in Unity also end up working on (some small) things like:
mouse input (raw input in Unity is garbage)
input controller
Character controller is super basic with almost no functionality other than simple movement
event system
Camera shake
…
No actual AI tools -> Why is there not a BT
Buggy UI…some panels grow/shrink when they shouldn’t
Terrain sewing
the list goes on