''Soldier'' -- Ellison deserved the credit he got
No question that The Terminator executed the idea with much more humanity, excitement, and interest. It's the superior work in every way.
However, there is also no question that the foundation of the first Terminator movie is Ellison's episode, "Soldier." From the opening with the laser beams to the materialization in the alley, to the idea of one "future soldier" stalking another, to the psychiatrist element, to the protection-of-the-humans bit... there simply would have been no Terminator movie without this episode. There are even bits of interaction with the Soldier and the kids that anticipate T2.
Is S2 really inferior to S1? I'll offer my assessment when I see more of it, but this first episode of S2 certainly seemed as good as all but the very best S1 episodes; better than 90% of them, especially towards the end of S1, when quality was clearly slipping badly.