Can the Federal Government be more efficient? Kind of. The trouble it, efficiency also costs more money. Musk didn't even come close to saving a lot of money, percentage wise of the budget. That should tell you something.
I don’t think it tells us anything, because I do not believe Musk ever undertook a good faith effort to improve government efficiency.
Love him or hate him, I think he did try and approach cutting programs from running a business as in "business-efficiency" mindset, with cutting middle management, using technology instead of people. What went wrong was:
Business exists to maximize profit and minimize waste.
Government agencies exist to achieve policy goals and enforces the nations laws. so the government can't cut "unprofitable programs" like defense systems that are maintained for redundancy or deterrence.
In other words a government is not a business that can just go in and cut things because they are not profitable or they cost too much money.
Helping the poor and other "wasteful" spending was granted by congress, congress decides not an administration.
IMO Musk came up against this and decided he had done what he could and moved on.