Looking back (hindsight) the decision not to evacuate was the correct one. It was not known at the time (foresight) if the decision would be correct or not.
And that's the point. It was not known it would be the correct one. That's why there are procedures in place, based on balance of probability, about what to do, if for example, a wing full of fuel is on fire. And those procedures are very clear. There is no risk assessment that could have said it would be safer to be on board, as soon as the fuselage is breached, people die. Unless the captain was recieving information from a psychic that that couldn't possible happen, it was the wrong call.
Aviation did not become as safe as it is by working on a philosophy of 'well no-one got hurt so it's all fine, nothing to see here.' Or are you saying BA maintanence procedures were fine before the engine cowl incident? No-one died so maintanence made the right call. The pilot made the right decision not to check they were latched? It's absurd logic.
I can't imagine there are many actual pilots here who could honestly say they wouldn't evacuate in such a situation. There also seems to have been zero guidance or instruction given to passengers either from flight deck or cabin crew (who I guess were waiting for their orders). With a wing on fire, no-one could have blamed pax for taking matters into their own hands, which might have ended very badly.