No, they were a greater threat based on HOW THE BORG REACTED. They just didn't bother going into their extended history, they didn't HAVE to. What matters is that the Borg took a heavier response to them than they EVER did with the Feds, which is Proof IN AND OF ITSELF that they were a greater threat. No further elaboration is needed.
Voyager created their weaponry based on simply using pre-existing Borg tech in a new way. The Borg KNEW that VOY couldn't turn something the Borg created pretty much on their own against them (all the VOY crew did was just redirect how that tech worked) and thus backed off. They had no reason to do anything else since they know that VOY can't easily replicate that weapon (if they can at all) to the extent of harming the Borg, if it can even harm them to begin with.
I know the weapon wouldn't have worked from "Descent". It doesn't matter if the episode came out later or not. And I know from other episodes that the Borg leave races alone and don't just assimilate everything in sight. This explains their behavior in FC as well in sending only one Cube.
What you refuse to see, is the big picture: When you have a force out there that can crush you easily but isn't bothering to because you're not worth the effort, you DON'T provoke them into attacking you with something you haven't even tested to see if it can really kill them beyond some engineers saying 'Theoretically it should kill them'. All you're doing is risking it all on something that may not even work with the greater probability of PO'ing this stronger force into thinking "f*** it, let's just kill this mofos and get them out of our hair once and for all." It's suicide.