Fortunately we don't need to rely on your hypothesis here; we can simply look at what's actually happening in the many countries where unions for software engineers are common.

Do you have actual examples of irrelevant jobs in software engineering that have been kept on because of unions? How about unions advocating for proprietary software in order to keep out open source software?

Given that many software unions already exist, the burden of proof is on you to prove that such things are actually happening. It's unreasonable to expect someone to prove the negative here.