Re: *Spoilers* Problems caused by the MCU
If they intended to not be really fantastical they failed in my eyes. Building a world-changing invention, that Stark Industries can't build with all their resources, with a box of scraps in a cave isn't exactly a grounded start.
Then basically going from a couple of small tests to trying out the suit as soon as it's ready in an extremely dangerous text, with all but perfect results, isn't exactly grounded either. Of course Stane, who hadn't even built anything, also got his Iron Monger suit to work perfectly the first time he tested it as well. Not to mention that the whole Iron Man suit concept isn't at all realistic to begin with as there's a ton of things about it that are impossible in real life.
It all works very well in the movie but in my opinion it's because it seemingly never tries to be something that's plausible in real life. It's a comic book movie through and through in my eyes.