Originally Posted by Big D
I figure Sisko was kept away from the fight for the same reason Picard was. As a man who once lost everything to the Borg, he could become an 'unstable element' in the fight due to fear or vengeance.
That, and keeping DS9's commander at his post would've been a high priority too.
That is a possibility, however, there might well have been several starship captains in the First Contact battle who would have been present at Wolf 359; they could well have lost families too.
I think the reason only applied to Picard, having been assimiliated by the Borg. The "unstable element", IMO, was a fear that he might be still vulnerable to Borg influence, and that fear was a reasonable one, particularly since, once the Enterprise
had joined the battle, Picard said to Troi "I can hear them".