When preparing for the Borg, Starfleet decides to do Wargames. Picard and his crew find these to be annoying due to that not being their primary mission and Starfleet has, at least up to that point, been capable of dealing with things with their usual Academy training. Riker was a clever tactician is noted in his record. The crew does acknowledge that the Borg are an issue, having faced them already. But Starfleet thought they had more time, at least another year or two, to prepare. With that time, and the Borg not assimilating Picard, would Starfleet have won? Possibly. The Enterprise by itself was figuring stuff out and surviving long enough to evade and report findings. The problem was because Picard knew all that stuff and gave the Borg an advantage over anything Starfleet had at that time. The Borge had shown no prior interest in such things, so that was a surprise to Starfleet and they didn't react to it quickly enough to save the fleet at Wolf 359, but the Enterprise still managed to work around the problem and came up with a solution.
