At the end of the game, when he transports the ship ten years into the future, to the time that the game began, he just so happens to bring the ship to a place right near an incoming Borg vessel. The characters point out that they're uniquely equipped to deal with the Borg and fly off to intercept. The whole point of the game was so that Q could plausibly put a Borg-worthy ship in that particular sector of space, to deal with that particular Borg ship, while maintaining plausible deniability about his true intentions. He only did all that stuff with Qaylan for his own amusement, after all....just messing with a human, like he does. And he brought the ship forward in time out of a sense of fairness and to avoid messing with the timeline, just like he said. He's very definitely not interfering with the war between the Federation and the Borg and I'm shocked you'd suggest such a thing. Just like his revealing the Borg to the crew of the Enterprise (and therefore the Federation) way before they should have known about them was him throwing a childish tantrum, and very definitely not designed to give the Federation an edge.
Q specifically brings back Quint before he leaves. Yet he doesn't revive Sprint, but instead treats it as if Sprint had died when he did before Qaylan took control of his body. If Sprint lived, that would mean all of the actions Qaylan undertook happened. Meaning the Borg would be aware of Bijani adrenaline and its ability to allow a 'borgified' person to retain their free will. If the Borg were aware of this, they would use this knowledge to protect themselves by destroying all Bijani on sight instead of assimilating them (as they do with Sprint once they realize he's 'defective',) or creating a way to bypass such 'compartmentalization,' and ensure all species are assimilated. Q specifically doesn't revive Sprint and lets him die when he was supposed to die to protect this knowledge from the Borg.
Or at least that's what I figured as a kid. Yeah, sure, technically, First Contact happens only six years after the Battle of Wolf 359. I just figured maybe all the characters were just rounding up. People do that sometimes, right?...
