You were extremely reasonable: didn’t ask for money, just address the issue – and they didn’t. If it’s worth the fuss (and it may not be), I might report their lack of interest in fixing the machine (or at least taking it out of service) to the Gaming Commission; then they might find reason to care 
If the machine is not operating within the parameters of GC’s regulations, they could be subject to a fine or, if it’s been programmed to take away some draws in certain situations, even worse.
The only excuse I can see from their point of view is that it costs money to take a machine out of service (lost revenue - and more lost revenue on a machine that’s not allowing big hands to pay off), and the attitude needs to be changed so that they expect it to cost money, and a lot more, if they don’t address it when necessary.
Meanwhile, don’t play there, or as you suggest, make big plays only with a witness! Personally, I’d opt for the former, since they might not care that you have a witness.
–BG
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Nothing happened! I got into a short conversation with a fellow later, telling him what happened. He said, “They don’t care.”
How can they not care? Somebody is going to raise a real stink, sooner or later.