I think your point of it being "reasonable" is subjective here, since there is no hard evidence in universe for or against your claim. Or, from a script writing perspective, if she even needed that ability since she can spam revive with basically no cool down or visible effect on her mana reserves. (which she did after the fight, right as darkness was having a softer moment, which resulted in her embarrassment and excellent comedic timing) You could also make the argument of why she can spam revive like that, and how that effects the tension in the story if death is merely a setback, but I just roll with it and appreciate it as a fun story.

I do agree that there is logical consistency, but I'm trying to make the point that you are assigning "good" and "bad" to various degrees of logical consistency, which is entirely subjective, and in your effort to try to make things "good" you infer "logical" conclusions without recognizing the subjective bias you have. (randomly pulling out a gun in a fight is bad because it diminishes the stakes - but that's totally OK in a comedy like konosuba, where a character spams revive to make death kinda pointless. You don't need serious life or death stakes to make a fun story, that's entirely your opinion. Or that aqua should have been able to dispel a curse despite having no knowledge on what are the capabilities of a priest, and one usually as useless as aqua)