"How the HELL did you manage to take over Voyager while we keep getting our asses kicked?"
Seska - who happened to be a Cardassian spy agent and 4 heavily armed carriers.
Realistically, if Kazon technology was outdated compared to Voyager (and depending by how much) - speculation indicated by several decades... then Voyager shouldn't have been taken as it was and could have went up against all 8 carriers seeing how Federation tecnology would evolve at an exponential rate in short periods of time (especially when you take into account 150 different races working together).
Granted... with Seska joining the Kazon, she already had some kind of knowledge of relatively advanced Cardassian and SF technology which she shared with Culluh (as indicated in the episode Alliances).
To Kazon credit, they had 4 heavily armed carriers going up against Voyager, which held on its own very well before that idiot Kazon blew himself up and impaired the ship's main power - otherwise, it would have probably been a victory for SF crew.
The writers took the Borg in a wrong direction by introducing the Queen (a limitation factor subject to making mistakes).
Aside from that... if the Borg encounter the Kazon, its likely they detect them from a large distance and simply avoid them.
Remember, the Borg wouldn't attack unless they see the opposing ship as a threat... so in that regard... they are less than a microscopic nuisance that couldn't do anything even if they wanted to (even Voyager had a tough time doing any damage most of the time and barely getting out of situations in one piece - only that was a more advanced ship).