The idea of robots going rogue has been done to death in movies is what I am saying. And the Ultron origin could be linked to Marvel continuity by Stark just stating here is an AI program that was designed b y Hank Pym that he left behind but I am playing with, etc. An easter egg if you will - but that is not here or there - having a killer robot turn on its human creator is as stale as one can get.
after rewatching it a bunch of times, i can say that ultron is one of the favorite MCU villains to date. (i haven't watch jessica jones so i can't give my thoughts on kilgrave, though i've heard nothing but good things)
Ultron being designed by some nobody with zero connection to the MCU Avengers would have made the story a lot weaker.
If Hank Pym can be the only one that created Ultron then Ultron would simply not have been in the movie and Stark and Banner would have created a different menace. Because it's not about Ultron. The big picture is about the development of Stark and Rogers. And considering that Hank Pym is actually in the MCU, and not a computer/robots guy, him creating an AI makes no sense anyway.
Killer robots turning on their creators are about as stale as superheroes saving the world or alien invasions or secretive government agencies going rogue. Superhero stories thrive on these ancient tropes.
Besides, I suspect that you would not find a Pym-created Ultron a Terminator rip-off at all.
My biggest issue with the use of Ultron was that it was a waste of James Spader. Much like it didn't make any sense to hire Christopher Eccleston to play a villain and then not give him any line chewing monologues to spout, or to hire Judy Greer to appear in a what was ostensibly a comedy and not give her any funny lines, hiring James Spader to be a speechifying villain and then burying his facial contortions and physical tics under a motion capture robot was a waste. The should ave used him to play Kang. A megalomaniacal world conqueror from the future would have been right up Spader's alley, plus Kang's costume wouldn't have hidden Spader's face.