The "size" of a coding task is not intrinsic to the task. It exists between tasks in the graph of their relationships. That is mostly hidden and changes over time.

This is why estimating software work is so hard, and why AI doesn't magically fix it.

Before AI, getting devs to write tests was painful. "Just let me merge this, I'll write tests later."

Now writing tests is gonna be the job! There will be much whining

The design -> code -> test loop is still fundamentally serial per feature. You can only use 100s of agents when your problem is embarrassingly parallel.