For this and many other reasons, government services should not be considered equivalent to a business and Elon Musk should not be considered any sort of expert in how to run them. I agree entirely with you. If Twitter goes down for a day and spends a month going up and down while Musk's kiddies fiddle with the scripts, it really doesn't matter. People who use the service essentially for free are not entitled to any guaranteed service level. Twitter may lose advertising due to the instability, but that's a decision Musk can make which hurts basically only him and those who agree to work for him.
When Elon Musk takes something as fundamentally different from a business as a sprawling government agency and slash it indiscriminately, it's not enough that he patently doesn't know what he's doing. There's a moral hazard. With Twitter, Musk's desire to tinker is limited by the amount of pain he's personally willing to endure in order to get it right—or to create the impression that he's getting it right. If he screws up a government agency whose primary purpose is to serve people who aren't him, he suffers no harm. Any time you are insulated from the consequences of your decision, that creates a moral hazard. Further, Musk's motives may even be counterproductive. He considers anyone receiving a government service to be a parasite. That's a perverse incentive.
I don't think anyone would honestly say that HHS isn't decentralized and inefficient. The key concept is that the services cannot fail. There is a tremendous cost borne by those served with the system fails to work. For that reason, the inefficiency is generally deemed more financially tolerable than wholesale system failure. But if someone comes along who simply ignores costs borne by others, this is what you get.