Realistically everyone is going to lose in every timeline if you wait long enough. If the Borg assimilated entire worlds during those centuries, what does it matter if they lose in some far point in the future? Won't undo the damage to the victims.I didn't buy the "always losing" thing just like I didn't buy the "it's not about perfect. You're lonely" thing. The Borg had a very long and successful career of assimilating other races. It was only relatively recently that they started losing to the Federation. Also, "losing in every timeline"? I don't know about that!
They oversold those points trying to make the persuasion more feasible. In the end, I can kind of buy the persuasion but more because Agnes is in there.