Better analogy would be Big Mom to Katakuri though in this case though lol. She fits mosts of the constraints you provide about Saturn here.
The issue is not necessarily that Saturn cant go down here, its about then what the WG manages to achieve by not getting Serephim and Mother Flame on their side, something thst is ultimately necessary for the WG to feel like endgame threats.
Also, this scene also seems to support that an escape scenario is still likely.
In order for an escape scenario to be the point, then it makes far more sense for Saturn to not actually lose here and command the destruction of the island