Sure they can cut a ton of people, they have already given notice to US AID; and yes there are programs that are crap, but US AID also is the US exerting it presence into developing countries. And when we stop providing assistance, then the China, India, Russia would but can't, will step in and gain or expand their foothold/influence around the globe. Also, note that US AID is also an agency that provides cover to US operatives (CIA, FBI, etc) - allegedly.
So if President TrumpMusk can pull the plug on that without even looking at any consequences; then they will damn near certainly layoff large groups that they don't understand what it is that they do. Musk was on the edge of bankruptcy several times at Tesla, and pulled a rabbit out of his hat; IMO he is way out of his league trying to fix the problems in US gov't organizations. Trump gave him this task as a reward for donating over $250 million to the campaign.