You answered the how he was defeated.
Not the why.
They knew it was a contracting wormhole because of dustin. They had the tower plan because of Steve. Theh executed the plan because of jane. They had all their gear they used because of Murray. They were able to locate him in the monster because of will.
Teamwork.. friendship. They won becayse they worked together as was the case every season.
Im sorry but when I read stuff like this its hard to take anything you say after seriously. Im really not trying to be rude here so I'm gonna pretend I didnt read that and move on.
They were planning on barreling through the military base, and making a clean getaway, they were not planning for the military to have become privy to their plans(which happened when Dr K and her men raided WSQK and captured Vicki and Max) which is the only reason K was present to ambush them
The why does not negate the weird boss fight.
Even so, the why is still weak. Dustin just stumbled into the room with the plans, Steve's plan of threading the other world by aligning a tower to a rift needs a whole book of excuses to make sense. They helped each other yes, but based on actions that make little sense.
Will literally had to accept he was a homo to use magical powers. He had to have a whole AA meeting with all of the characters, while the world was about to end, to be able to use them. He did use magic by accepting his internal homosexuality.
Nancy gunned down a bunch of soldiers and they busted through the gate. The military would obviously be ready for them to return. They were high-fiving and making jokes as they crossed through the gate.
And then, Nancy, after killing all these people, gets a free pass. In fact, Sarah Conner and the evil military lets everything slide.
Hopper, who spent the season killing military personel, gets reinstated as a police officer.
Now, I didn't hate this, it's not some horrible show, but it's incredibly stupid and poorly thought out.