Striker is a more advanced combat suit. I would not go to prototype level, but why not... after all it was a last chance all out attack by the alliance when Ledo and Kugel didn't secure their grip during the subspace leap and ended on earth. So I guess even a prototype could be used in such a circumstance. And Striker could be one of those suits with a very advanced AI that can make choices...

I do not think however Striker chose to let Kugel die in his sleep or from the disease, that twist also has been overused, but that would fit that botGod which doesn't value human life that much.
The choice might have been:
Humans never have been able to win the war. I'm the first generation of bot able to make choices and I'm better than humans at everything. Why should I support one, when I can do better alone. Solution/choice: get rid of humans to have the job done... (Kill all Hideauze)

But of course, maybe life support was limited in time, after all Ledo had been waiting for 6 months when he woke up and we do not know how long he lived on Gargantia, but something like a year would be plausible.

Maybe a time limit would be 1 year and Kugel wasn't able to survive after that, unable to find food/water?
Then Striker finds that fleet with a cultists tyranny, so it just has to come at the top...