Even if that is true, a lot of business software is not public and not in the training set.
And another thing to consider, is if you are copying software from another business you need to compete in some way. Yours needs to have more polish (LLMs are bad at this), or a unique feature, or a different focus. LLM copying another business will only allow you to compete on price, but not those other things.
I think the premise of the argument is you don't need to compete in the marketplace because you can just tell the robots what you want and they will happily produce it.
The fallacy that people are making is they look at the current state of things as 'the way it'll always be' while the AI companies, and I mean all the AI companies, are looking to corner the market so have no moral issues with taking out a whole swath of skilled jobs.
The cost to compete with another business's software is a high-end GPU.
And another thing to consider, is if you are copying software from another business you need to compete in some way. Yours needs to have more polish (LLMs are bad at this), or a unique feature, or a different focus. LLM copying another business will only allow you to compete on price, but not those other things.