Ricky_Bobby: Yes it really surprised me too, his character was memorable, I struggle to recall what the main character even looked like. I think it was a mistake to pit a relatively unknown actor and actress against Arnold.
I still regret that the original pitch of the movie never materialised. I remember reading way back, that there was an idea for the movie to be about a retired soldier close to the Connor family (played by Arnold), so badass Skynet later used him as a template for the T-800. The movie was to be set in the 50s or something like that, and be about Skynets attempt to kill Sarah Connor's mother, with Arnold's character protecting her.
Of course there is no telling if it would turn out good, but it sounded more interesting than the mess Genisys turned out to be. And since Arnold actually showed some acting chops in this one, having him play an actuall human being rather than a robot might have worked really good.