If you jump off of the flying fortress you land in the city below............
And you land near a tiny park. You're stuck in this tiny park unless you do the Doc Oct mission. If you leave the park, everything is cordoned off and you can only cross the street to enter one building. This is not a short mission - it's multiple stages [inside and outside, with advanced moves required] and if you don't finish the entire thing, you start out back on the fortress.
I think you guys are misremembering, because in no way does Marvel start out open world. There are multiple, long, difficult [for younger ones] missions in the way.
Meawhile, again, Lego CIty undercover just starts you out in open world, like I said. The first mission in LCU is just 'go to the police station', which you can avoid doing for as long as you want.
1 mission before you're on the flying fortress, but lol.
Might as well just play Lego World instead of any of the games with stories.
Except you still aren't at the open world after beating the mission with Sandman and getting to the fortress [which isn't a short mission to begin with], as per above.
And this all started because I specifically said Undercover was great for little kids. Why are you being so damn condescending, especially when you're wrong? He doesn't care about the story if he can't get to it.