Regarding tightness in FC, the whole story is bull****. The Borg want to invade Earth, but then they actually want to go back in time to invade Earth when there's no Federation, but then they actually want to stop First Contact, but then what the queen had in mind was actually to persuade Data to join the ranks. Those are four different plots and villain intents, they are not interchangeable.
... A villain having having multiple plans and approaches is a problem
I'm sorry, I really can't wrap my head around this: If any of those plans interfered with each other, or if the script had forgotten about any of them at any point, then you might have a point, but it doesn't.
If you want to go back in time and invade Earth when it's vulnerable, do so far away from any nagging starfleet ship that may enter your slipstream.
If you want to stop First Contact, you... don't need to. If you invade Earth ten years before that, there is no First Contact.
If you wanted Data to join the ranks, weren't there better ways to do so?
Oh no, the villains' plan has a weakness
, what a glaring issue!
I mean, if you're arguing on that level, pretty much any story where villains are thwarted is nonsense and bad. Why doesn't Obadiah Stane just shoot Tony Stark, or hire a thug to do that?
Why doesn't Khan just ram the Reliant into the Enterprise to disable her, then kill Kirk in one-on-one combat?
Why doesn't the Empire make sure the reactor room of the second Death Star is thoroughly shielded and armored first?
It's not that you cannot argue around every instance of the plot, which I guess you can to a point, it's the constant barrage of unjustified turns akin to children's playful narratives "I'm gonna destroy you with this giant robot! Ahah you wished, my powerful gun smashes it to pieces! Oh yeah? Surprise I have a hidden sphere I pulled from the robot's ass! Oh yeah? my ship is gonna football it! Surprise my sphere TRAVELS THROUGH TIME ahahah you didn't see that comin! Oh yeah? My ship will follow you and blow you to pieces! Oh yeah?
By the time they change their plans by the fifth or sixth time, I've already checked out from the movie.
Yeah, no, I don't see a single instance of an "unjustified turn" in this movie. Or, for that matter, any real change of plans.