If you're going to use a spreadsheet as your UI, I think you should be more careful how you describe the semantics of rows and columns. And make a strong case for why this representation makes sense.

People expect that rows represent observations and columns represent variables. Along those lines, would it not be more accurate to say each row represents an instance of a task and column represents a sub-task or step in that task?

"each row corresponds to an AI agent executing a task" just... doesn't make sense. The rows exist before you press the "execute" button, after all. The agent executing the (generic) task is something that happens on or with the sheet.