Are you out of your fuckin' gourd?! Sisko not battle-tested?! Sure, maybe it wasn't a great way to start his intro at the Battle of Wolf 359 or whatever the fuck number it was, but afterwards he kicked ass left and right, sometimes in a runabout! He had the Defiant, which was a ship and eventually lead hundreds of other ships into kicking the Dominion straight in the balls!
He's not battle-tested my ass.
And to go back on another subject, true K, he is weak on diplomacy. But there really wasn't a call for it at the edge of the quadrant. Now I'm not saying Sisko didn't have any, 'cause he had to have had some to work well with Bajor and calm those Cardassians down.