Batman is rarely the level of plot of Deathstroke, who stands no chance against the wall bending Squirrel Girl. She is the embodiment of irreverence and fun that most comic geeks have to shed off for office work and daily toil. Characters like Squirrel Girl win to keep things fun. She brings the funny to every title she is in. To be brief, she is Falstaff with feats.
Bruce gets to master all martial arts and learn alien technology in minutes, get with beautiful women that die so often he should view himself as a walking std, and have most of his dialog be with himself in his own head(gifting us with his inner goodies). Against most cosmic beings whose power is expressed through pretty splash pages, going up against a character whose popularity and therefore existence is sustained by their musings of the situation is a very mighty task. If Bruce muses a plausible sounding win scenario, you better believe it will happen almost exactly like that after his initial thrashing to build tension.
The battle goes to SG because Batman's brooding cannot sustain itself on the light and happiness that will overwhelm the angst and resolution in depression that gives his narration power. Heroes around SG become happier, and that will break batman worse than Bane could ever dream.
It a sad day when zoom and flash are put in the same category as spectre, phantom stranger, and mxy... Also, isn't kirby basically a walking pink black hole? If so, he is a threat (not saying the team will win just deeming him a threat).