The Incredible Hulk Isn't A Good MCU Origin Story
One of the most underappreciated parts of the Marvel formula, and why their origin stories tend to follow such a similar structure in the first place, is how the films focus tightly on the hero and establish how they'll work in upcoming sequels and team-ups alike. They establish the character's personality, their defining ethos, their power-set (normally all reflected by a mirror villain) and by the end how they integrate into a team-up is done. From Iron Man to Ant-Man, this has worked incredibly well, meaning when we get to an Avengers or Captain America: Civil War, there's no need for character realignment.
The Incredible Hulk simply doesn't do that. The origin is skipped over in the opening credits, likely because it's so well known and was last seen in 2003 (a similar approach was taken for Spider-Man in Homecoming), so the Bruce we meet is on the run and skittishly defined. But what stands out most is how little is given about Hulk's abilities and temperament in preparation for how he would work with the Avengers. Even at the end of the film, he's still an unknown; that could offer up an interesting arc for Norton with a re-edit but in the MCU leaves a feeling of aimlessness.
It's telling that the Bruce Banner we got in The Avengers onwards had an entirely different attitude, although the main character is just part of how the setup didn't go anywhere.
The Incredible Hulk's MCU Setup Proved Wrong
Of course, The Incredible Hulk became so unimportant to the MCU after the recasting of Bruce Banner, with Mark Ruffalo replacing Edward Norton in The Avengers. However, while this (and the lack of return from Liv Tyler's Betty Ross or Tim Blake Nelson as an overtly teased The Leader) are typically the go-to examples of how disconnected it is, it's more a sidenote compared to the world building.
The Incredible Hulk is full of references to Stark Industries, S.H.I.E.L.D. and super soldiers, and its ending is directly building to The Avengers: Banner gains control of turning into the Hulk and Tony Stark visits General Ross to talk about a team he's building. There's one problem - it's not setting up The Avengers we got. The Hulk is being positioned as a threat that S.H.I.E.L.D. wants to contain, suggesting a more direct adaptation of Avengers #1 (which has Loki using Hulk to create havoc), and Tony is forming Earth's Mightiest Heroes, a responsibility removed from him in Iron Man 2 (the stinger is retconned by short film The Consultant to be a deterrent to keep Abomination under lock and key). Plainly, the gameplan set in 2008 was completely changed, and the pivot is right at the core of The Incredible Hulk.
That the early shared universe would have some course correction is hardly surprising; so much was in flux at the emergent Marvel Studios and the ability to adjust was key to long-term success. This was produced concurrently with Iron Man, and much would change to The Avengers as it developed and Joss Whedon reworked it. But The Incredible Hulk nevertheless shows just how little there was in terms of big narrative beyond "they team up".
But beyond the story, it's clear that in terms of relation to the past (comics or TV show), other blockbusters and the core of the character, The Incredible Hulk was out of step with the MCU as it became. And while it's easy to point to it as a mistake from Letterier or Universal (who still own distribution rights to Hulk), it's more an immortal emblem of how little Kevin Feige and co. really had planned out. That's not a criticism, more a fact of moviemaking on this level. If anything, that the direction was so unclear makes it all the more impressive that, in a few short years, The Avengers redefined everything.