Amdahl's Law says the speedup you get from throwing more workers at a problem is capped by the part that can't be split. You can run a thousand agents in parallel and still sit there waiting on the one commit that has to happen in order. It's the same as a company hiring a thousand engineers and still grinding to a halt because one person/team understands the deploy script.
Parallelism doesn't kill the bottleneck. It just clears everything else out of the way until the bottleneck is the only thing left standing, lit up, impossible to ignore. The more you speed up the easy parts, the more obvious it gets that the slow part was always the drag.
Most of what we call "scaling" is just elaborate work to avoid looking straight at the one step we never wanted to deal with. We'll automate, distribute, and optimize around it forever, because that feels like progress, and staring at the actual problem doesn't.
Solving and optimizing for that is the real efficiency-unlock.
