Naah, you nailed it in one. Starfleet is portrayed pseudo-realistically in TOS as sometimes engaging in deliberate aggression in the name of diplomacy, sometimes holding back for the very same reason. In "Corbomite" and "Spectre of the Gun", Kirk has orders to break in, guns blazing; in "Balance of Terror" he has to mind his every step; in "A Taste of Armageddon", he is but a chauffeur to a diplomat who calls all the shots until emergency protocol applies, at which point it's guns on hot again.
This is not a contradiction. Different opponents no doubt require different treatment in order for the diplomacy to be effective. Kirk's standing orders seem to err on the side of reckless violence rather than caution, though, as he engages the First Federation territorial defenses without knowing of them in advance or having specific direct orders. But he very much chooses guns over retreat, while freely admitting to being in violation of a territorial claim.
Would Maxwell's crew have a reason to believe in a different set of standing orders? The Cardassians are the enemy; news of interaction with them requiring the velvet gloves now might not have reached anybody but the starship COs, because it should be a big secret that Starfleet is suffering from strategic weaknesses in the region and for that reason pussyfooting around.
The Jem'Hadar wanted for the big starship to die yet for the runabout witnesses to retreat. Nothing was stopping Kirk from retreating - all his maneuvering commands referred to trying to get past the cube, rather than going back to where they came from, after all. That the cube would give chase should hardly be taken as sign of blocking retreat, then.
Timo Saloniemi