The Defenders: 10 Reasons It's A Massive Disappointment
2. There's No Need To Team Them Up
Tied very closely to the fact that half of The Defenders feel a little shoe-horned into the plot, there's no real justification for why these superheroes would come together in the first place. The threat isn't big enough to warrant extraordinary measures (and Daredevil or Iron Fist could probably deal with it all themselves), and the stakes feel a lot higher with Jessica Jones and Daredevil's first seasons in particular.
That's the value of a big charismatic villain with a grand plan.
There's not even that much pay-off from the rest of the supposedly establishing series. Sure, there's a continuation of The Hand story, and Elektra's return (which is just one and the same really), but little else that shaped those seasons pays off here. They're brought together by and for convenience, not by an MCU-like entwined grander narrative.
Also, if the stakes are this high and if the world is in magical danger, where is Doctor Strange? If there are suspicious tremors threatening to destroy everything, where is Tony Stark? Obviously we weren't going to get any of the Avengers, but as soon as the show fails to adequately solve the question of why they wouldn't turn up, it invites the question even more.
On a more general level, some of the writing is awful. That counts for both broad strokes like the big plan at the film's climax being "let's blow up Midland Circle"