There are practical limits to efficiency. I have worked in both the public and private sector in my decades long career, and I can't say that private efficiency is that much better than public efficiency.
I disagree. Maybe you've worked in more efficient government agencies, but I've worked in both sides and the private industry groups Ive worked with arent perfect but are massively more efficient.
There is waste in private enterprise to be sure. The key difference is that that mostly punishes people who voluntarily invested and can choose to stop investing if they get fed up with it. That's (practically?) not at all the case in terms of federal government waste.
What makes that the key difference? Doesn’t it depend on what you care about?
The voluntary part is the key difference from a libertarian perspective, but it is not the most important bit if your goal is to, say, minimize suffering for the worst off in society.