The current autocomplete behavior dictates that when you hit the right arrow key, the current suggestion is fully instantiated including all arguments. In many cases this behavior makes autocomplete useless, for example if I type 'w' for 'wget' and hit right arrow, I get wget+the link of whatever I downloaded last, which I then must delete before I can paste a new link. I've ended up typing out 'wget' manually instead simply because it's less work. Ideally, autocomplete should only complete to the next whitespace, and then push the cursor onto the first character of the next suggested argument without actually selecting it until you hit right arrow again. That would also make browsing through history items with a filter (or browsing complete options by typing) require fewer keystrokes.

There are some cases where one-argument selection behavior might make things slower, but I think it's acceptable as long as the behavior is consistent (which it currently doesn't feel like it). Rather, the current autocomplete behavior with directories works intuitively, but for commands does not.