Please explain how this "improvement" happened without the "laborers"
Those are just the low hanging fruits without any major impact to how work is done.
Stepping down into the internals of the business, it’s going to vary a lot but in manufacturing you spend time looking at high failure rate processes, bottlenecks, and single points of failure. Changing these with effectively no change to how individual laborers work is quite common and can significantly improve yield stability and throughput.
Going even lower level, it might be as simple as better insulation around a bake process resulting in 50% less energy.
You might be interested in reading about the improvements in steel mills where the labor required was reduced by an order of magnitude over the last 50 years: https://en.wikipedia.org/wiki/Steel_crisis
Improvements come without labor all of the time and it’s a frequent point of contention with the labor when it eliminates a role rather than acts as a force multiplier.
I couldn't have explained worker alienation better had I tried
The laborers made more money because of your idea while performing the same work. They are better off and still had no part in making the improvement.