If they said that the Borg ships in VOY were all smaller and weaker, I'd buy that explanation.
In fact, I can still
buy that explanation even though it didn't exist. Like I said, that's part of suspension of disbelief... You can retcon the story to make it make more sense, but you can't claim that that was deliberately a "subtle" part of it in the first place. That's ludicrous.
No, they tried
to make us believe they had tougher, scarier ships, but then ended up making them feel less threatening. That answers the question in this thread's title.