For the love of all things good, stop it with the damn origin stories.
F4 doesn't work because it's fundamentally boring and bullshit. When you have Reed build an Ultimate nullifier out of his ass you just know even the writers don't give a ****.
They also share a problem I have with the X-men, their powers are so singular and uncreative to the point that you can't do anything interesting with them. Cyclopes is the most easy example of this, he shoots or he doesn't shoot. Unless you count his powers of being a dick, that's all he's got. Its why in all the movies they keep picking Wolverine as the focus point, compared to everyone else he is multifaceted and more importantly, easy to write for.
They could have picked Storm, but her powers are more grand and hard to use in a budget effective way like slapping plastic on to some hands. Throw in the fact they ditched her African origins and cast Hallie Berry showed they had no confidence or ability to write for such a character which is basically anything not a white straight male with varying levels of gruffness.
It doesn't help I am burned out on super hero movies since it is pretty much watching the same movie over and over again while taking crazy pills.
I think an origin story for Fantastic Four can work. They just can't make it like they have known each other for only 2-3 years.
If you are dealing with a family then make them act like a family...let them trust each other even when they are made at each other. Don't just tear them apart to make stupid drama. Give them relationships where the audience doesn't know their inside jokes, because we aren't on the inside. Have them already be close. Family relations are quite interesting when you write them carefully. If I was to do Fantastic Four, Reed and Sue would already be married. The team would pretty much already be together in a working relationship and then they go up into space. I think there is an interesting story to tell about them arguing about if they keep their powers secret or not...and how they use them. Is it for science, for heroics, or not all. Don't spend time with them fumbling over there powers like every super hero movie.
As for the X-men. I guess I disagree. I like the singularity of their powers, because it makes them being a team important. Superman doesn't need a team...he has so many powers it is unnecessary. Same with Wonder Woman, Green Lantern, Martian Manhunter, Firestorm, Cyborg, Doctor Fate.
What I always disapproved of, was some of the mutant powers that make no sense. Storm is a perfect example. How does one evolve to control the weather? It is a cool power, but insanely impossible for a mutation...and actually just dumb. The global impact on her abilities is stupid. However, most of the original team was very cool and believable.