Wow thanks for the detailed feedback! This is super useful. I don't have time to respond to each point but it's all really good info.
I will say that the random cube in level 4 is actually part of the intended solution for the bug, though I'm not happy with how I implemented it. Beyond that everyone is just brute forcing it by bridging the gap with the bug.
Intended solution:
There's a tiny hole in the wall behind the bug (the small cube obscures this). You've got to make the duck super small and push it into this hole (the small cube helps with this, it's fiddly. Then you scale the duck up and it pushes the cube with the bug on to an accessible point. Definitely replacing or editing this one anyway.