If anything getting not only tortured but straight up slashed with a lightsaber would realistically reaffirm every fear he had about getting killed. Which is exactly where he starts in TLJ.
You see there you go saying things again, when did Finn move past this line?
Inverting implies that he moved past this in the film, or that this is proper motivation to want to fight:
after literally spending an entire film running away so that something like this wouldn't happen.
If you think the message of Canto Bight was "both sides" and that everything is grey then you weren't paying attention. If only there was an entire sequence where the film says, "yes no this whole Canto Bight war profiteering thing is bullshit"