Instead, they irresponsibly just left them out there waiting for their next invasion.
Like this, you mean?
SPOCK: "I can't help wondering if there are any more of those [planet killers] wandering around the universe."
What are you talking about? How were any of those wrapped up? Who built the probe and the planet killer? Where's the rest of the species the jellyfish belong to? Genesis wasn't inherently flawed, it was only flawed because of the unauthorized shortcut David took. And there are tons of other examples.
VOY had them in the Borg homeland, it wouldn't make sense for them NOT to repeatedly show up.
The Delta Quadrant wasn't Borg Homeland any more than the Alpha Quadrant was the homeland of all of the above. Both of them are a quarter of the entire galaxy
VOY was under no continuity obligation to have Voyager come across the Borg, they merely had greater opportunity
-- an opportunity which according to you, they shouldn't have taken at all... yet they did, so I once again bizarrely find myself
in the position of defending VOY against your
arguments, which are becoming more and more flimsy by the post.