Though I agree with much of what you wrote, it is my belief that this movie marked a change in direction for the series. Much like after Star Trek IV where humor was felt to be necessary in order for a good trek movie.
Again, I find your premises faulty. Star Trek First Contact was a piece in the Borg story arc that had started during the second season of the TNG series (Q Who?). Also, humor has always played a very important role in Star Trek starting way back with the TOS series (Shore Leave, Trouble with Tribbles, I Mudd , A Piece of the Action, just to name a few.)
Yeah, Picard could always throw down when the situation called for it. I mean, the Klingons respect him, for crying out loud. What more proof do you need? He kicked a lot of ass on the series. It didn't seem far-fetched to me that he was such a badass in FC. It was a very chilling moment, though, when he killed that ensign.

How can a movie that was such a huge success critically and at the box office drive a stake into the heart of Trek. For myself I think First Contact is not only the best TNG film but also the best of all the films.
As far as focusing on Picard and Data, Generations did that as well. TNG made a good use of its cast on the tv show where everyone had episodes that featured them. Remember though that each episode generally focused on one ore two characters not the whole cast. The two most popular and most used characters in the show overall were Picard and Data. It was an ensemble show but those were your two main characters and in a two hour movie you've got to focus on the main characters, you can't have 7 subplots going on.
I also think that although First Contact is an action flick it was heavily focused on Character. I thought The Borg queen's seduction of Data was fantastic and Picards ahab turn was also great.
You are free to have your own opinion but this movie was a huge success and not the start of the end for trek.

Warmest Wishes,
Whoa Nellie