Although it's said to be a direct time-loop, it's implied that Skynet in Terminators 1 and 2 had different motivations.Does skynet still have access to Time Travel?
If it does it can use it tactically to preempt any single act on the Ceph's part.
Also, while skynet was not all that intelligent in the movies Terminator:TSCC had units that were quite autonomous.
In 1, it was said (in the novels and creators' comments) that it felt actual horror that it committed near-genocide, when it learned more about the world. When it launched the nukes and took control of the existing infrastructure, it simply didn't, well, know any better.
However, because of how it was hard-coded, it couldn't simply kill/end itself; additionally, the same directives meant it couldn't simply give up to the Resistance or make it "easy" for them -- it had to seriously attempt to destroy them.
It was basically trying to "suicide by cop" while resisting said cops as much as possible.
Obviously this has major flaws though, such as why it sent a T-800 back in the first place, unless those same directions basically forced it to try to survive even when it didn't want to. shrug
This Skynet was implied to be like a computer that had peripherals plugged into it (e.g. tanks and aircraft as mice and keyboards).
In 2, it learned rapidly upon coming online and quickly became self-aware -- when the USM panicked and tried to shut it down, it nuked everyone (and used the counter-strikes from Russia and other nations) to remain online as a form of self-defence. It knew exactly what it was doing.
It's a bit paradoxical because you can have a bit of sympathy for Skynet (it was just trying to stay alive) and horror at its actions, as it was pretty malicious.
"To stay alive, I must not just kill the people trying to shoot me, but I must also kill the entire town."
This Skynet was implied to be more of a networked machine, e.g. computers on a network, than the "peripheral model".
Of course, when we get into Terminator 3 and above, Skynet is malicious and genocidal from the get-go, even when it has the opportunity to not be (such as when it was the Genysis Operating System in T:G) -- it chose to kill mankind than trying to escape its "fate" by acting dumb and playing nice/the long game.
What's worse is that every iteration of Skynet after T1 became more and more advanced as the proverbial can was kicked further down the road: it started off as a supercomputer with peripherals and ended up as being a cloud-based super-intelligence that already had access to the modern world.