Software is the classic example of how you can not simply add workers and get s faster result. It is kind of like trying to get nine women to make a baby in one month. Some things need to be done serially and you need time to iterate and review, and rework.
With software, it is the quality, not the quantity of workers. OK, an exception is testing. you CAN put a ton of people on that and find problems fast. But then you have to assign bugs to engineers and track the fixes and fold them all together, this is a bottleneck that is hard to speed up.
What you want is a smaller number of smarter workers. In software, in any small group of about 6 people you will find the best is twice as productive as the average. There is a large diversity of productivity