It's all about the execution. Iron Man 1 was nothing special. Guy gets to see what his weaponry does to the world and decides to use his brain and tech to fight it back. Iron Man 3 broke the mold and it was really different. Is Iron Man 3 a good film? I don't know. I liked it. It's not that bad as some people make it look like, but despite being different and creative, it's not as good as Iron Man 1.
Iron Man 1 was special, because it basically defined the now typical superhero origin movie which we have seen at least a half dozen times in the six year period since, but before that, it had not been seen once before in the previous six years. Execution is a necessary factor, but being a well executed version of something that is constantly being well executed anyway doesn't get you very far.
Iron Man 3 is a good film at 78% fresh. Avenger also broke the mold, as did The Dark Knight. You know what films didn't break the mold at all? Green Lantern and Captain America The First Avenger. Even Thor and Batman Begins played around with the chronology a bit. So being not utterly typical is another necessary factor.
You want both. Iron Man 1 had both, it was not typical because of the time frame it was released in AND it was well executed. Having just one leads to a much more limited success. Saying it's all about the execution is like saying it's all about the actors. Yes, you need great actors, but you also need a good script. If the script is lousy, you may not even be able to get good actors. Likewise, if you don't have a fresh idea, then you may not get even the people working on the film excited enough to do a great execution. No one gives their all to make Iron Man-lite.
Yes, as you said the other time, ''they could be lying'' is probably not a good argument. But it doesn't mean they're telling everything. Like I said that time, you can't expect them to spill it all during an interview. I'm not saying Stark won't have a hand on Ultron. All I'm saying is it's not going to be that simple. With the reports of the AoU crew filming in locations such an old hospital and that scene in the 40s with Bettany, Evans and Atwell, I won't be surprised if Ultron's origins come from something the Avengers and those related to them did through all those years. I recall Scarlett Johanson giving a brief description about the film, with ''past catching up to these characters''. That would make it more interesting than Tony Stark deciding to create a new AI.
I never excluded other elements being involved. But when someone is asked a question, and they give a direct answer, but the truth is that the answer is different, I call that a lie. If I ask you what kind of shirt you're wearing, and you go on to describe how red your shirt is, I'm not going to look for the guy with the red and blue striped shirt. When we meet, and I say 'Oh, I thought you said a red shirt' and you say 'well, there was no reason to assume that I gave you all the information, and besides, I wanted to surprise you' I'm going to, inwardly, curse your savage cruel idiocy and never trust anything you say again, since you answer direction questions with verbose half truths, which is no truth at all.
Stark creating the Ultron AI will be just that simple, because to complicate that part is a waste of space. Now that AI going bad, and how different aspects of the team's history makes that happen, that will be interesting to watch, but it will not change who creates Ultron, which is why when asked about that, we are given Stark references. Because when it comes down to who makes Ultron, there's only one reasonable answer. It's not until we ask who makes Ultron free or who makes Ultron evil that we start to get into the interesting part, and even then, it still comes more from the Avengers we know, and less from, y'know anyone else.
Because if you say your shirt is mostly red and come to find out it's equally red and blue, I might actually curse out loud.
To be honest, I don't think this is going to be a big problem. We're not going to see the team filled with 20+ people. Rotating the roster makes the Avengers something really cool.
Even rotating the roster, the big 4 cover a lot of ground. Fitting someone into that is a challenge.