I don't get why people think the fans think the Borg were too powerful.
It's like being annoyed that in every story the man who steps on the ant succeeds in killing it. That's not making a man too powerful, it's taking seriously the parameters of a situation.
Sure there are stories in which ants reek havoc on humans and some of them work and some of them suck. The problem with the Borg stories isn't that the Borg were just too powerful, it's that the stories sucked.
If part of the reason the Borg hadn't yet taken over the entire galaxy was that large portions of them were constantly being sent to take over the Delta Quadrant's version of the Metrons or Organians or Vorlons or what have you, ancient super-powerful aliens the Borg were slowly wearing out over thousands of years and countless drones, that'd be pretty darn cool. Sure they were losing mind-boggling amounts of material...it may take another hundred thousand years to complete assimilation of a species - from our perspective the Borg are in check (by then there may not be any humans or Romulans left in the galaxy given how species rise and fall) but still it paints the Borg both in check and really terrifying.
Instead, what happens:
- The Borg are defeated by 8472 - whose claim to fame was wrinkly cells.
- The Borg didn't even use nanoprobes initially. Why not assimilate 8472 by chopping off their limbs and installing microchips in their brains like everybody else? And those rinky-dinky nanoprobes were embarrassing.
- Other aliens could stay one step ahead of the Borg by being good linguists. Brilliant.
- Other aliens weren't considered smart enough to be assimilated. WTF? Rip off their heads and use their bodies for manual labor. You're the horrifying BORG for chrissake.
- The Collective becomes a fickle goth chick with favorites and moods. ...In a little-black-dress and ponytail hair without the ponytail.
- Spheres and Tactical Cubes are toyed with.
- Queens killed left and right.
- Drones liberated or otherwise disconnected from the Collective left and right.
- Ex drones were not scary at all but hot chicks who moved in with you and went to human charm school.
The Borg weren't too powerful - they were too popular and the ratings were low. They were de-fanged by crappy writers/producers in an imploding franchise.