I remember how menacing the humanoid robots were in the the initial movie.
I was a bit older and wiser by the 2nd movie.
1. The movie and ticket buying audience is 100 % human, thus they would relate to human likenesses on both the good and bad sides of the movie.
2. The Hunter killers zoom around a battlefield quickly attacking the resistance fighters. The machines like efficiency, and should have produced many more of them. Not only that, the film shows how difficult it was for the humans to counter against them.
3. The humans rely on food, which the machines do not need. The Machine web logs should have had examples of how the US railroads and cavalry slaughtered the buffalo herds in order to impoverish and eventually subdue the plains indians.
4. Humans can be poisoned by gasses in ways that would not effect the machines.
5 The machines should have poisoned all of the available surface waters.
By the 2nd movie, when you had that morphing metallic alloy machine, it should have been way over for the human resistance of the future.
6. Why bother keep humanoid forms and sizes for those types of machines?
Those types of machines could have kept forms that humans do not watch out for , such as liquid carpet, rolling rocks, raccoons, cats, mice, whatever the minimum size is to carry a high detonation level bomb to the remaining human group shelters.
If the machines can make one, they will soon be able to make many more.
Total machine victory could be achieved within 3 years of that development.
Time machining another assassin robot (with the special morphing capability) was not neccesary.
Human sized robots with big weapons, is a stupid way of letting the human resistance groups defeat a few, and then start arming themselves with the range weapons that you made. The machines should have realized that calculation early on.