Originally Posted by Ant-manic
it's too early to tell what will or won't be rational. if, for some strange reason, Pym is appearing only in flashback or a retiree in the Ant_man movie, it'd might not be as logical to use him as Ultron's creator.
i don't see how it'd be superfluous to Stark. it'd be the logical next step in his evolution. he starts out as the best weaponeer on the planet. he sees how dangerous these weapons can be in the hands of others. he fights to take those weapons back.
next part of the story involves others trying to replicate his weapon and Tony discovering a higher purpose (thanks to his father's recordings).
then comes extremis; human "iron men."
next...the weapons, themselves, gaining sentience i.e. Ultron
Ultron would become Yet Another Killer Robot. And general audiences and movie critics alike would correctly point out that Stark will have already been there/done that with the drones in IM2 and with Extremis-powered suits in IM3.
The last thing Tony Stark needs to build in the MCU post-IM3 is another robot/drone/suit that takes on a life of its own.