You are clearly missing the essence of this conversation as "foolishness", "stupid" and "dumb" are all words that are considered ableist.
What you are saying is that the use of the word "retarded" is viable because it means "foolishness". However, the word "foolishness" shares the same baggage as "retarded".
You use another synonym to mean that the company does not have the intelligence and awareness required to monetize its invention properly.
Reread this sentence that you wrote: "I think simply "retarded" is also effective and concise, uttered not in a spirit of wanton bullying, but rather for the purpose of vivid illustration of behaviour that is, in fact, profoundly stupid."
Now ask yourself what the vivid illustration you are painting is.
In the end, it boils down to a simple fact. The use of these words will hurt some people and discourage others from interacting with you.
Trying to justify their uses does not come off as mature but as resentful and bad-tempered. Especially in a professional setting.
Imagine talking to a business leader who has a child with special needs that is called "retarded" on a daily basis. You may be in a job interview where the interviewer happens to be on the austim spectrum and regularly has to deal with people who call them "retarded". What about a CEO who is struggling with bipolar disorder and whose actions are described as "foolish"?
In all of these cases, you are hurting or discouraging someone with your choice of words.
It may not be in the spirit of gratuitous bullying, but the words still carry meanings. They stigmatize an already marginalized population. They carry meanings you may not be familiar with yourself but that others are very intimate with.